Bus converted to a motorhome, 230v side of things - I am fitting a selector switch so the user can select between "inverter-off-mains" for supply to the 230v installation. Part of the installation is a 230-12v charger for charging the house battery. I am wanting to inhibit the charger from running from the inverter. The two options I am weighing up are a 4 pole changeover switch - using the 4th pole as a switch for the charger, or a 3 pole changeover switch and fitting a din mount contactor with it's coil connected to the inlet cable so once energised the charger circuit is closed via the contactors contacts. (A bit cheaper) Can I connect the inlet lead to the changeover switch and then loop over to the contactor coil without further OC protection? Is there an issue with this route?
Cheers
Charger inhibit when running on inverter
Re: Charger inhibit when running on inverter
It's entirely possible to use a contactor as you suggest; but it makes complying with some of the other requirements more complex.
For example; the supply to contactor coil is effectively a subcircuit (or part of one), because it supplies a load. Therefore it must have RCD protection.
You also have to provide current limitation on incoming supply.
Both these can be complied with by using an RCBO, usually after the c/o (as shown in Fig 3.1 of "3001"). In this position the RCBO is effective both when on external supply and when supplied from inverter. It's the origin of the (single) final subcircuit supplying all loads; and as long as you don't have any reduction in CCC no further over-current protection is required. Even if you do have a reduction in CCC, generally the overcurrent device can be omitted under "3000" clause 2.58.33.4(b)(ii). Eg the 6A mcb shown in Fig 3.1 for the lighting circuit is not actually required; as the lighting will be all directly-connected fixed loads (and these days lighting is mostly ELV d.c.).
However you can't branch anything off upstream of the device(s) that provide these 'universal' functions - even if it's only supplying a contactor coil or an indicator light - without needing to add more protection devices. The current limitation function must control ALL loads; and ALL parts of final subcircuits must have RCD protection.
You could move the RCBO to be upstream of the source selection; and loop off to a contactor coil from the load side.
But then you won't have RCD protection on anything when supply is from inverter (since you're planning for a 3-pole source selection switch; I assume the inverter isn't RCD-protected ex-factory).
So you'd have to add another RCD downstream of the source selector.
For simple set-ups where all loads are on a single final subcircuit, you only need a single RCBO; which can also act as "main switch" and as current limiter. But as soon as you start splitting loads so that some are supplied only from one particular source; more protective devices are required.
Next edition of "3001" will include more guidance on possible configurations for using multiple sources of supply However it keeps the underlying requirements of absolute current limitation for each incoming supply, and RCD protection for all parts of all subcircuits.
For example; the supply to contactor coil is effectively a subcircuit (or part of one), because it supplies a load. Therefore it must have RCD protection.
You also have to provide current limitation on incoming supply.
Both these can be complied with by using an RCBO, usually after the c/o (as shown in Fig 3.1 of "3001"). In this position the RCBO is effective both when on external supply and when supplied from inverter. It's the origin of the (single) final subcircuit supplying all loads; and as long as you don't have any reduction in CCC no further over-current protection is required. Even if you do have a reduction in CCC, generally the overcurrent device can be omitted under "3000" clause 2.58.33.4(b)(ii). Eg the 6A mcb shown in Fig 3.1 for the lighting circuit is not actually required; as the lighting will be all directly-connected fixed loads (and these days lighting is mostly ELV d.c.).
However you can't branch anything off upstream of the device(s) that provide these 'universal' functions - even if it's only supplying a contactor coil or an indicator light - without needing to add more protection devices. The current limitation function must control ALL loads; and ALL parts of final subcircuits must have RCD protection.
You could move the RCBO to be upstream of the source selection; and loop off to a contactor coil from the load side.
But then you won't have RCD protection on anything when supply is from inverter (since you're planning for a 3-pole source selection switch; I assume the inverter isn't RCD-protected ex-factory).
So you'd have to add another RCD downstream of the source selector.
For simple set-ups where all loads are on a single final subcircuit, you only need a single RCBO; which can also act as "main switch" and as current limiter. But as soon as you start splitting loads so that some are supplied only from one particular source; more protective devices are required.
Next edition of "3001" will include more guidance on possible configurations for using multiple sources of supply However it keeps the underlying requirements of absolute current limitation for each incoming supply, and RCD protection for all parts of all subcircuits.
- Rating: 16.67%
Re: Charger inhibit when running on inverter
Thanks for that AlecK. How about a RCBO for the mains, and another for the inverter? - come off the load side of the mains rcbo before the selector. Label both RCBO's as "Main Switch"?
Cheers
Cheers
Re: Charger inhibit when running on inverter
RCBO for external supply can be upstream of source selection device.
2nd RCD to cover supply from inverter can be either upstream of source selection device, or downstream.
Upstream is better.
Either way you'll have RCD protection in place regardless which source is selected.
However when it comes to issuing WoEF, both RCDs will need to be tested.
If both are upstream of selector - one on each feed to the switch; no problem, as each can be tested separately.
But if one is downstream, then it will be difficult to test both without having to make alterations, then re-instate after testing.
So better to avoid having one RCD upstream of another.
--------------
There are a lot of fancy inverter/ chargers available these days; including automatic change-over.
But they generally don't comply with the requirement to have isolation between the loads and the off-load source
Refer 3.4.4.3: "when one source is connected to the electrical installation, the second source is isolated with respect to all live conductors from the installation.". This aspect also requiring to be tested every WoEF [C 7.8.1].
Which means that the selection switch needs to be an isolating switch.
Also needs either a 460 V rating, else have an "off" position between the two "source selected" positions.
The question then becomes whether the internal switching if these units provides 'isolation"; and the answer is "almost certainly not".
While some special contactors can provide isolation, most can't. Nor can relays.
2nd RCD to cover supply from inverter can be either upstream of source selection device, or downstream.
Upstream is better.
Either way you'll have RCD protection in place regardless which source is selected.
However when it comes to issuing WoEF, both RCDs will need to be tested.
If both are upstream of selector - one on each feed to the switch; no problem, as each can be tested separately.
But if one is downstream, then it will be difficult to test both without having to make alterations, then re-instate after testing.
So better to avoid having one RCD upstream of another.
--------------
There are a lot of fancy inverter/ chargers available these days; including automatic change-over.
But they generally don't comply with the requirement to have isolation between the loads and the off-load source
Refer 3.4.4.3: "when one source is connected to the electrical installation, the second source is isolated with respect to all live conductors from the installation.". This aspect also requiring to be tested every WoEF [C 7.8.1].
Which means that the selection switch needs to be an isolating switch.
Also needs either a 460 V rating, else have an "off" position between the two "source selected" positions.
The question then becomes whether the internal switching if these units provides 'isolation"; and the answer is "almost certainly not".
While some special contactors can provide isolation, most can't. Nor can relays.
- Rating: 16.67%
