Looking at a comment in Electrolink

This includes types of overcurrent, Short Circuit and RCD protection
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DougP
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Looking at a comment in Electrolink

Post by DougP »

May-July
Page 18, third column

"Cheap 230V MCBs are often used on three phase installations but some electricians don't realise that they could end up with 400V across them"

Yes, some "domestic" MCBs are marked as "230V", and some have a little picture of a house on them, but the specifications tell the real story.


https://eref.se.com/au/en/pdl/product-pdf/DOM11378

https://www.nhp.com.au/files/editor_upl ... OD6106.pdf
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Re: Looking at a comment in Electrolink

Post by AlecK »

This "inadequate voltage rating" is a myth commonly raised by the half-educated.
Disappointing to see it being promulgated by a group of inspectors; as they should know better.
But hardly surprising.

Old-time Inspectors had no special training at all.
Then the first under the 1993 Regs only had to have "deemed adequate experience" .
And while modern Inspectors at least have to pass an exam, it only covers one aspect of being an "Inspector".
Then while "competency" courses for inspectors are supposed to include content specific to inspection / Inspectors, few actually do
As a result, there are a significant proportion of people who hold "I" Reg & PL, but in fact are barely fit to hold "E" Reg.
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Re: Looking at a comment in Electrolink

Post by JamieP »

How would you get 400V across them anyway? Regardless of the rating values

You'd only ever have 230V to E wouldn't you? Being single phase your only going to have a single active through them
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Re: Looking at a comment in Electrolink

Post by DougP »

If you use them for a 3ph load, then with one or two turned off, it could have up to 400V across it.
And I guess technically, if one circuit breaker out of 3 on a 3phase circuit trips, it is breaking to an open circuit voltage of up to 400V.

But yes, mostly they are used on single phase circuits, even as part of a 3 phase installation.

Obviously even without having to dig deeply into manufacturers specifications, or the requirements of the standards that the circuit breakers are built to, we should be able to assume that they are all rated as suitable to use on our 230/400V MEN system of supply.
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Re: Looking at a comment in Electrolink

Post by AlecK »

For loads connected in "star" there's only ever 230 V across the mcb contacts.
For loads connected in "delta, yes there's 400V between phases but each "leg" of the load is across 2 mcbs; effectively in series.
The Un stated is the nominal voltage; ie 230 V to earth. So you can put a 30 V device hard up against a sheet of earthed metal, and it's insulated for 230 V. That's the same for the next one along as well, so in effect the insulation rating between 2 adjacent 1P mcbs is 460V.
The only real difference with eg Schneider's "domae" range is that some of the more high-end tests specified for mcbs (eg Type 2 co-ordination with other switchgear) have been omitted - in order to reduce cost tyo end-users who don't need that level of functionality. But all the basic tests for overload & short circuit functions have been done.
So while they may not be up to serious industrial work, particularly for motors; they're perfectly OK for low-end commercial / industrial work such as lights & sockets. Regardless of whether the circuit is single or multi-phase.
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Re: Looking at a comment in Electrolink

Post by PawPatrol »

DougP wrote:
Mon Jul 13, 2020 10:43 am
If you use them for a 3ph load, then with one or two turned off, it could have up to 400V across it.
And I guess technically, if one circuit breaker out of 3 on a 3phase circuit trips, it is breaking to an open circuit voltage of up to 400V.

But yes, mostly they are used on single phase circuits, even as part of a 3 phase installation.

Obviously even without having to dig deeply into manufacturers specifications, or the requirements of the standards that the circuit breakers are built to, we should be able to assume that they are all rated as suitable to use on our 230/400V MEN system of supply.
Hi,

Be careful, if the fitting isn't labelled that it can handle a voltage, how can you assume that it can?

In New Zealand RCDs are required to be labelled with the voltage they are designed for.

If the RCD doesn't say 400, or 230 for that matter, it means you can only assume that the labeling is correct and you can't assume it is suitable for something else.

This also includes 240 V labeling - no good for New Zealand.
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Re: Looking at a comment in Electrolink

Post by AlecK »

The voltage rating marked on the mcb is the operating voltage (Ue).
If it's marked for 240 V , then it's perfectly OK for use on 230 V nominal.

There are 2 IEC Standards for mcbs, with different performance requirements in a number of areas.
Domae & similar are designed/ built / tested to one; whereas other ranges are generally designed/ built / tested to both

There's certainly NO problem using "domae" & similar for single-phase circuits on a non-domestic setting - although it may fail earlier (ie after fewer operations)

There's also no issue WRT having several single-pole devices adjacent to each other on a chassis / busbar, as each is rated to be against an earthed metal sheet and in effect there is (at least) 460 v worth of insulation between the conductive parts of adjacent single-pole mcbs.

Whether they can be used on 30phase circuits is where there may be an issue,
coming down to whether there will ever be more than the marked voltage across the contacts.
You'd need to study the relevant IEC standards for full details
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Re: Looking at a comment in Electrolink

Post by DougP »

PawPatrol wrote:
Fri Jul 17, 2020 8:17 am
Hi,
Be careful, if the fitting isn't labelled that it can handle a voltage, how can you assume that it can?
In New Zealand RCDs are required to be labelled with the voltage they are designed for.
If the RCD doesn't say 400, or 230 for that matter, it means you can only assume that the labeling is correct and you can't assume it is suitable for something else.
This also includes 240 V labeling - no good for New Zealand.
Did you open any of the links I posted?
domae.jpg
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Re: Looking at a comment in Electrolink

Post by PawPatrol »

The regulations don't consider what they have on their web site, but rater what the product says.
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Re: Looking at a comment in Electrolink

Post by AlecK »

Rubbish.
The regulations don't care about what labelling is on product (except eg voltage rating of appliances in ESR 23). They just say the product has to be safe.
But because mcbs are DMRAs, they have to have an SDoC (which states what product Standards they comply with);
And if we know the standard(s); the products comply with; we can find out a lot more about the product than just what the labelling it happens to have on it says.

In fact, without the product Standard, we often couldn't even tell what a marking (for example) actually means.
An mcb has several different voltage ratings, not just one. they include the "rated insulation voltage (Ui), the impulse voltage (Uimp), and the rated operational voltage (Ue) .
Using this "Domae" mcb as example, it is marked "230 V"; but without any indication of which voltage rating is being referred to.

For some products, the relevant standard will dictate what Markings must be shown - but most of us don't have easy access to these Standards
Instead we have to use the product data sheet. after all, that's what it's for.
Data sheets include a lot of relevant info that's never going to be marked directly on the product
They are just as valid as on-product markings when deciding what to install; in fact more so because of all the extra info.
Though only the SDoC provides us with any legal bum-cover at all.

In fact, by looking on the data sheet, we now know that this mcb complies with Part 1 of IEC 60898; which is a Standard for mcbs intended for use in domestic / small commercial installations. Full description:
IEC 60898-1:2015+A1:2019 applies to a.c. air-break circuit-breakers for operation at 50 Hz, 60 Hz or 50/60 Hz, having a rated voltage not exceeding 440 V (between phases), a rated current not exceeding 125 A and a rated short-circuit capacity not exceeding 25 000 A.
These mcbs perform the basic functions of Isolation & Protection against overcurrent

Industrial mcbs are generally also compliant to IEC 60947-1 & 60947-2; and have additional functionality.

There are 3 other relevant markings on this example device; but without the data sheet we have no idea what they actually mean.
But with the data sheet, we know that "DOM11378" is the catalogue number (which is how we get the correct data sheet);
"6000" is the fault current rating; and
"C20" is a combination of the rated current and operating curve.

So with a "230 V ~" marking; and a data sheet saying : "Ue rated operational voltage : 230 / 400 V AC 50/60 Hz"
and "breaking capacity: 6 KA at 230/400 V AC 50/60 Hz conforming to IEC 60898-1"
there's absolutely NO problem using these on a 3-phase circuit.

But what I wouldn't do is use them on DC, even at ELV; because there's nothing to suggest they're suitable for that.
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