Mobile Medical 6115
Mobile Medical 6115
Hi, has anyone had any experience with continuous earth monitoring in a mobile medical installation? what actually is it and how does it work? any links would be much appreciated.
Re: Mobile Medical 6115
Bender is one supplier of the device required by NZS 6115.
There is a NZ agent and thay have supplied monitoring devices for existing Mobile medical installations.
There is a NZ agent and thay have supplied monitoring devices for existing Mobile medical installations.
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Re: Mobile Medical 6115
Start by reading App A, clause A3; which includes additional information.
And Fig 4 includes one
While A3 talks about "requirements"; because App A is classified as Informative it can't set requirements; it's only guidance.
The actual requirement - set by 1.5 for units with > 12 mA total leakage - is simply "additional means of earth fault protection".
So it doesn't have to be continuous earth monitoring; other systems may be used - though not clear what counts and what doesn't.
I've struck earth monitoring only once, back in the late 1970's; and that one was installed long before I came on the scene
The basics are the lead to the appliance - or for "6115" the mobile medical unit - has an extra conductor,
which allows a monitoring circuit to continuously monitor that the PEC remains intact and connected.
If the PEC goes above max permitted resistance, supply is cut off.
The monitored equipment could only be used on the socket that had the monitor, because of course it requires an extra pin on the plug, and a matching socket.
And it only monitors from the socket outlet, because of the high risk of damage to connections of flexes to portable equipment
(which was even greater back then, with the old metal plugs, sockets, and connectors).
So there's still a risk of losing the PEC of the circuit supplying the socket outlet; but that being fixed wiring the risk is less.
My recollection is that the monitoring back then wasn't very sophisticated; not much more than a relay
with the coil held in by a circuit through the PEC and pilot wires.
These days I'm sure they are electronic; but the principle will be the same:
making sure that the PEC for the item in question remains continuous, and doesn't have excessive resistance.
The system in A3 is different; instead of the monitoring device being at the socket, it's within the mobile unit
That may be intended to reduce cost; as only one monitoring device per unit needed, instead of one per site.
The sites get the other half of the system; being a resistor and diode (or whatever the particular monitoring unit requires) to complete the monitoring circuit via PEC & pilot wire.
-------------
What I find strange is that while this additional protection is required, and therefore must be presumed important for safety;
there's nothing in Section 7 to require testing of such systems either as part of WoEF, or at the various sites as part of PA under ESR 75.
Not that ESR 75 requires PA of these sites. It requires PA of what's "in" the mobile medical facility, but not for the site the MMF plugs into. I suspect that's an error within the ESR.
-----------
Earth continuity monitoring is also "required" by the Worksafe guidelines for (some) EV charging systems; and will be part of the PA for public charging stations.
And Fig 4 includes one
While A3 talks about "requirements"; because App A is classified as Informative it can't set requirements; it's only guidance.
The actual requirement - set by 1.5 for units with > 12 mA total leakage - is simply "additional means of earth fault protection".
So it doesn't have to be continuous earth monitoring; other systems may be used - though not clear what counts and what doesn't.
I've struck earth monitoring only once, back in the late 1970's; and that one was installed long before I came on the scene
The basics are the lead to the appliance - or for "6115" the mobile medical unit - has an extra conductor,
which allows a monitoring circuit to continuously monitor that the PEC remains intact and connected.
If the PEC goes above max permitted resistance, supply is cut off.
The monitored equipment could only be used on the socket that had the monitor, because of course it requires an extra pin on the plug, and a matching socket.
And it only monitors from the socket outlet, because of the high risk of damage to connections of flexes to portable equipment
(which was even greater back then, with the old metal plugs, sockets, and connectors).
So there's still a risk of losing the PEC of the circuit supplying the socket outlet; but that being fixed wiring the risk is less.
My recollection is that the monitoring back then wasn't very sophisticated; not much more than a relay
with the coil held in by a circuit through the PEC and pilot wires.
These days I'm sure they are electronic; but the principle will be the same:
making sure that the PEC for the item in question remains continuous, and doesn't have excessive resistance.
The system in A3 is different; instead of the monitoring device being at the socket, it's within the mobile unit
That may be intended to reduce cost; as only one monitoring device per unit needed, instead of one per site.
The sites get the other half of the system; being a resistor and diode (or whatever the particular monitoring unit requires) to complete the monitoring circuit via PEC & pilot wire.
-------------
What I find strange is that while this additional protection is required, and therefore must be presumed important for safety;
there's nothing in Section 7 to require testing of such systems either as part of WoEF, or at the various sites as part of PA under ESR 75.
Not that ESR 75 requires PA of these sites. It requires PA of what's "in" the mobile medical facility, but not for the site the MMF plugs into. I suspect that's an error within the ESR.
-----------
Earth continuity monitoring is also "required" by the Worksafe guidelines for (some) EV charging systems; and will be part of the PA for public charging stations.
Re: Mobile Medical 6115
Found details in the 1976 Regs; in Notes to R 103.
Description & Fig confirm what I recalled; main points being
- LV: ELV transformer, out via PEC 1, to appliance, back via PEC 2, to n/o push-button, to contactor coil.
In those days the extra PEC was often the CBS sheath of the appliance flex
I'm sure the device referred to in A3 is far more sophisticated; but anyone could build the old type and it would comply with 1.5
Wouldn't have auto-livening , must be manually reset; but that's not important.
I suspect much cheaper; and very easy to test.
Description & Fig confirm what I recalled; main points being
- LV: ELV transformer, out via PEC 1, to appliance, back via PEC 2, to n/o push-button, to contactor coil.
In those days the extra PEC was often the CBS sheath of the appliance flex
I'm sure the device referred to in A3 is far more sophisticated; but anyone could build the old type and it would comply with 1.5
Wouldn't have auto-livening , must be manually reset; but that's not important.
I suspect much cheaper; and very easy to test.
Re: Mobile Medical 6115
The issue for the customer is that they would have to update all their sites. Funnily enough we went to visit an existing mobile screening unit and it had no earth monitoring equipment, so maybe the equipment wont have more than 12mA. Thing is, you don't know what the leakage will be until you build it!!
Thanks for all the info, very very useful
Thanks for all the info, very very useful
Re: Mobile Medical 6115
With the simple system (and I expect with the ready-made unit); important that each PEC have separate connection at each end
Re: Mobile Medical 6115
The simple circuit earth monitoring unit from the 1976 handbook is not good enough.
The existance of a diode as part of the sensing circuit should tell you that the clever box required has some more checks and balances built into the continuous monitoring circuit.
From memory the monitoring circuit uses half wave pulses so that the checking required is better than a simple series circuit and not confussed by normal earth circulating currents.
In large mobile medical installations the combined level of earth leakage currents does not permitt the use of a single 30mA RCDs.
So mobile medical installations relie on a good earthing connection to remove the leakage currents. You must also remember that AS/NZS 3003 requirment also need to be covered so the final option was a bit of a mix of AS/NZS 3003 and some new material in NZS 6115.
I was on the drafting committee for NZS 6115 and was the author of appendix A.
The existance of a diode as part of the sensing circuit should tell you that the clever box required has some more checks and balances built into the continuous monitoring circuit.
From memory the monitoring circuit uses half wave pulses so that the checking required is better than a simple series circuit and not confussed by normal earth circulating currents.
In large mobile medical installations the combined level of earth leakage currents does not permitt the use of a single 30mA RCDs.
So mobile medical installations relie on a good earthing connection to remove the leakage currents. You must also remember that AS/NZS 3003 requirment also need to be covered so the final option was a bit of a mix of AS/NZS 3003 and some new material in NZS 6115.
I was on the drafting committee for NZS 6115 and was the author of appendix A.
Re: Mobile Medical 6115
you may not consider the simple system good enough.
And I fully accept that the system referred to in A3 is superior.
However facts are that
1 there is nothing in the Standard that makes that superior system mandatory; and
2 the simple system fully complies with the requirement stated in the clause.
If that's not what was intended; it should have been written better.
And I fully accept that the system referred to in A3 is superior.
However facts are that
1 there is nothing in the Standard that makes that superior system mandatory; and
2 the simple system fully complies with the requirement stated in the clause.
If that's not what was intended; it should have been written better.
Re: Mobile Medical 6115
AlecK
I wish to correct a post you made in a statement which is incorrect.
I quote from your post
However facts are that
1 there is nothing in the Standard that makes that superior system mandatory; and
2 the simple system fully complies with the requirement stated in the clause.
If that's not what was intended; it should have been written better.
Quote ends
Taking your points seperately
1. The system device specified (AS/NZS 2081.2) comes from the mining industry.
2. NZS 6115 clause 2.8 requires the earth wiring monitoring system to comply with AS/NZS 2081.2.
As clause 2.8 is in the main body of text details the SHALL requirement which is common standards drafting practice.
Appendex A is informative and that is OK as background information, as clause 2.8 contains the SHALL requirement.
I wish to correct a post you made in a statement which is incorrect.
I quote from your post
However facts are that
1 there is nothing in the Standard that makes that superior system mandatory; and
2 the simple system fully complies with the requirement stated in the clause.
If that's not what was intended; it should have been written better.
Quote ends
Taking your points seperately
1. The system device specified (AS/NZS 2081.2) comes from the mining industry.
2. NZS 6115 clause 2.8 requires the earth wiring monitoring system to comply with AS/NZS 2081.2.
As clause 2.8 is in the main body of text details the SHALL requirement which is common standards drafting practice.
Appendex A is informative and that is OK as background information, as clause 2.8 contains the SHALL requirement.
Re: Mobile Medical 6115
My statement that "the simple system fully complies with the requirement stated in the clause" is clearly with reference to clause 1.5.
And is absolutely correct in that regard.
OK, I accept that 2.8 makes it mandatory for monitored earth systems, when installed at service pillars, to comply with the Standard.
But because that clause is in Section 2; it can only apply to service pillars and supply leads .
For a similar requirement to apply to MMFs; it needs to be in Section 3 .
Or, more sensibly - since any monitored-earth system system has aspects that affect both the pillar and the MMF itself - it should have been in Section 1.
That would have been following the "common standards drafting practice" you refer to.
Instead, you put a very general & open requirement into 1.5; mentioning monitored earth only as an example.
Having two related, but different, requirements in different Sections, with no cross-reference; is not only against all logic but contrary to "common standards drafting practice".
And by failing to follow the usual conventions, you have failed to implement the intent.
The end result is that (for MMFs with > 12 mA leakage):
[1.5] some , unspecified, form of "additional means of earth fault protection" is required for both MMFs, and supplies to those MMFs
monitored earth is mentioned s an example; but anything in addition to the specified 100 mA RCD complies
[2.7] the "additional earth fault protection" for the pillar (but not for the MMF itself) must be either double insulation or continuous earth fault monitoring of the lead and fittings. Either choice is compliant.
[2.8] if the monitoring option is chosen, then the system must comply with "2081.2" (again only for the pillar, and not for the MMF itself)
---
So you have specified what kind of system can be fitted into the pillar / lead.
Yet the Fig shows a system that's more correctly described as being installed into the MMF; for which there is no corresponding requirement set in Section 3.
That creates at best a lack of clarity; but - more likely - confusion for most readers.
True, logic says that if the pillar has part of a monitoring system installed; the MMF should have the other part.
But Standards are not supposed to rely on logic; they are supposed to tie up all loose ends and remove any possibility of an unwanted option.
while allowing all acceptable options.
In practice; the only factor that ensures the two halves of the system match up is the additional pins of the supply lead plug.
If the monitoring system was in the service pillar, non-monitored MMFs would not be able to obtain a supply .
By installing the monitor into the MMF (as per Fig 4), both monitored and non-monitored MMFs can plug into the socket on the pillar.
So even more reason for the requirements to be mentioned in Section 3.
-----
Similarly, if adopting the other option of double insulation; that requirement can also only apply to the pillar, and not to any part of the MMF.
All normal flex is classed as double insulated; as are the '60309" plugs & connectors of the supply lead.
Job done; full compliance achieved for MMFs with > 12 mA leakage.
(even if the pillar isn't DI; because the requirements only apply to " the supply lead and the supply lead fitting earth connections").
Why would anyone feel inclined to go further?
The answer is that DI of the lead doesn't significantly reduce the chances of the lead PEC going open-circuit.
IMO, DI should never have been an acceptable option, because it simply doesn't address the risk
(DI of the entire MMF , including all equipment plugged into it, might; but that's not what the requirement specifies)
So if someone did want to go further than minimum compliance by DI; there would be nothing unlawful about exceeding the minimum requirements - including by adding a (non-required) earth monitoring system.
The requirement for earth monitoring systems to be of a particular type can only apply where that is the chosen option for mandated "additional earth fault protection".
As an optional extra; anything that doesn't conflict with fundamental safety is acceptable
And there's nothing remotely unsafe about the simple sort of earth continuity monitoring described in the 1976 Regs.
------
That's just some examples, relevant to this discussion, of the many deficiencies in this particular Standard.
Another glaring error - though not directly relevant here - is in the Exception inserted by Amendment 2;
with specifies a "maximum" IP rating for "3123" plugs / sockets , when what matters is the "minimum" rating.
Epic fail by whoever wrote that!
Poor writing in a poor layout, combined with few clause headings; makes it difficult to find anything.
IMO it needs to be completely re-written; by people with a better grasp of how to do it.
And is absolutely correct in that regard.
OK, I accept that 2.8 makes it mandatory for monitored earth systems, when installed at service pillars, to comply with the Standard.
But because that clause is in Section 2; it can only apply to service pillars and supply leads .
For a similar requirement to apply to MMFs; it needs to be in Section 3 .
Or, more sensibly - since any monitored-earth system system has aspects that affect both the pillar and the MMF itself - it should have been in Section 1.
That would have been following the "common standards drafting practice" you refer to.
Instead, you put a very general & open requirement into 1.5; mentioning monitored earth only as an example.
Having two related, but different, requirements in different Sections, with no cross-reference; is not only against all logic but contrary to "common standards drafting practice".
And by failing to follow the usual conventions, you have failed to implement the intent.
The end result is that (for MMFs with > 12 mA leakage):
[1.5] some , unspecified, form of "additional means of earth fault protection" is required for both MMFs, and supplies to those MMFs
monitored earth is mentioned s an example; but anything in addition to the specified 100 mA RCD complies
[2.7] the "additional earth fault protection" for the pillar (but not for the MMF itself) must be either double insulation or continuous earth fault monitoring of the lead and fittings. Either choice is compliant.
[2.8] if the monitoring option is chosen, then the system must comply with "2081.2" (again only for the pillar, and not for the MMF itself)
---
So you have specified what kind of system can be fitted into the pillar / lead.
Yet the Fig shows a system that's more correctly described as being installed into the MMF; for which there is no corresponding requirement set in Section 3.
That creates at best a lack of clarity; but - more likely - confusion for most readers.
True, logic says that if the pillar has part of a monitoring system installed; the MMF should have the other part.
But Standards are not supposed to rely on logic; they are supposed to tie up all loose ends and remove any possibility of an unwanted option.
while allowing all acceptable options.
In practice; the only factor that ensures the two halves of the system match up is the additional pins of the supply lead plug.
If the monitoring system was in the service pillar, non-monitored MMFs would not be able to obtain a supply .
By installing the monitor into the MMF (as per Fig 4), both monitored and non-monitored MMFs can plug into the socket on the pillar.
So even more reason for the requirements to be mentioned in Section 3.
-----
Similarly, if adopting the other option of double insulation; that requirement can also only apply to the pillar, and not to any part of the MMF.
All normal flex is classed as double insulated; as are the '60309" plugs & connectors of the supply lead.
Job done; full compliance achieved for MMFs with > 12 mA leakage.
(even if the pillar isn't DI; because the requirements only apply to " the supply lead and the supply lead fitting earth connections").
Why would anyone feel inclined to go further?
The answer is that DI of the lead doesn't significantly reduce the chances of the lead PEC going open-circuit.
IMO, DI should never have been an acceptable option, because it simply doesn't address the risk
(DI of the entire MMF , including all equipment plugged into it, might; but that's not what the requirement specifies)
So if someone did want to go further than minimum compliance by DI; there would be nothing unlawful about exceeding the minimum requirements - including by adding a (non-required) earth monitoring system.
The requirement for earth monitoring systems to be of a particular type can only apply where that is the chosen option for mandated "additional earth fault protection".
As an optional extra; anything that doesn't conflict with fundamental safety is acceptable
And there's nothing remotely unsafe about the simple sort of earth continuity monitoring described in the 1976 Regs.
------
That's just some examples, relevant to this discussion, of the many deficiencies in this particular Standard.
Another glaring error - though not directly relevant here - is in the Exception inserted by Amendment 2;
with specifies a "maximum" IP rating for "3123" plugs / sockets , when what matters is the "minimum" rating.
Epic fail by whoever wrote that!
Poor writing in a poor layout, combined with few clause headings; makes it difficult to find anything.
IMO it needs to be completely re-written; by people with a better grasp of how to do it.
Re: Mobile Medical 6115
Pluto
Would suggest that you read the whole of the standard and stop “cherry picking” clauses and get the full extent of the requirements.
Part AK quote
So you have specified what kind of system can be fitted into the pillar / lead.
Yet the Fig shows a system that's more correctly described as being installed into the MMF; for which there is no corresponding requirement set in Section 3.
Pluto comment
The correct section of NZS 6115 to use is “5. Connectable installation switchboard and supply connection configurations. This Section also covers the use of generating sets as an alternative supply source, so all the switchgear in the MMU switchboard is located under a common heading, which is logical.
In NZS 6115 section 5 the clauses cover the following:-
5.1 No N to E link in MMU switchboard.
5.2 Switchgear and neutral connections required for a permanently wired “On – board “generating set.
5.3 Switchgear, neutral and plug/socket connections required for a “portable generating” set.
5.4 No back feed from generating set to the mains supply connection and vice versa.
5.5 Minimum voltage rating of the mains/generating set changeover switchgear.
5.6 Minimum current voltage rating of the mains/generating set changeover switchgear.
5.7 Requirements for 3 phase installations with equipment that is phase rotation sensitive.
5.8 The continuous earth wire monitoring system, what it controls and the limits or trip points of the monitoring system.
The only missing item is the reference to AS/NZS 2081.2 .
Part quote AK
That creates at best a lack of clarity; but - more likely - confusion for most readers.
True, logic says that if the pillar has part of a monitoring system installed; the MMF should have the other part.
Pluto comment
A MMU unit which this standard at the top end when earth leakage currents exceed 12 mA is a complex installation and is capable of operating from a number sources; mains supply from service pillar, or a generating set (either “on board” or a plug and socket connected “portable”) providing the supply.
Would suggest that you read the whole of the standard and stop “cherry picking” clauses and get the full extent of the requirements.
Part AK quote
So you have specified what kind of system can be fitted into the pillar / lead.
Yet the Fig shows a system that's more correctly described as being installed into the MMF; for which there is no corresponding requirement set in Section 3.
Pluto comment
The correct section of NZS 6115 to use is “5. Connectable installation switchboard and supply connection configurations. This Section also covers the use of generating sets as an alternative supply source, so all the switchgear in the MMU switchboard is located under a common heading, which is logical.
In NZS 6115 section 5 the clauses cover the following:-
5.1 No N to E link in MMU switchboard.
5.2 Switchgear and neutral connections required for a permanently wired “On – board “generating set.
5.3 Switchgear, neutral and plug/socket connections required for a “portable generating” set.
5.4 No back feed from generating set to the mains supply connection and vice versa.
5.5 Minimum voltage rating of the mains/generating set changeover switchgear.
5.6 Minimum current voltage rating of the mains/generating set changeover switchgear.
5.7 Requirements for 3 phase installations with equipment that is phase rotation sensitive.
5.8 The continuous earth wire monitoring system, what it controls and the limits or trip points of the monitoring system.
The only missing item is the reference to AS/NZS 2081.2 .
Part quote AK
That creates at best a lack of clarity; but - more likely - confusion for most readers.
True, logic says that if the pillar has part of a monitoring system installed; the MMF should have the other part.
Pluto comment
A MMU unit which this standard at the top end when earth leakage currents exceed 12 mA is a complex installation and is capable of operating from a number sources; mains supply from service pillar, or a generating set (either “on board” or a plug and socket connected “portable”) providing the supply.
Re: Mobile Medical 6115
Some other background.
There was considerable common sense applied by the team of nine committe memebrs in the preperation of this standard in 2006.
There was no IEC, BE, EN, or UL standard to follow for the MMU and we started from a blank sheet of paper, and developed this standard in a very short time frame to cater for the building of a large number of school dental clinics about to commence construction.
I also checked if AS/NZS 2081.2 is still current but it hads been superseded by AS/NZS 2081:2011.
There was considerable common sense applied by the team of nine committe memebrs in the preperation of this standard in 2006.
There was no IEC, BE, EN, or UL standard to follow for the MMU and we started from a blank sheet of paper, and developed this standard in a very short time frame to cater for the building of a large number of school dental clinics about to commence construction.
I also checked if AS/NZS 2081.2 is still current but it hads been superseded by AS/NZS 2081:2011.
Re: Mobile Medical 6115
Of all that, the only relevant item is 5.8.
Which as you admit, does not require compliance with any Standard.
5.8 sets only 2 requirements: "the incoming main isolating switch shall be trip if the supply lead earth wire resistance is outside preset limits".
However no such resistance limits are set; and there is no requirement that there must be a "main isolating switch"
either in "3001" for CIs in general, or in "6115" for MMFs in particular
As I said, "6115" is a mess
Which as you admit, does not require compliance with any Standard.
5.8 sets only 2 requirements: "the incoming main isolating switch shall be trip if the supply lead earth wire resistance is outside preset limits".
However no such resistance limits are set; and there is no requirement that there must be a "main isolating switch"
either in "3001" for CIs in general, or in "6115" for MMFs in particular
As I said, "6115" is a mess