Suitability of circuit accessories.

[Leezo]

Hi all,

Hopefully this is being posted in the right place, apologies if not or if my question has been previously answered.

I'm currently having a bit of a disagreement with my supervisor having carried out an inspection which is for all intents & purposes, a condition report on a living quarters within a military base.

I have reported a 32A single phase circuit feeding 2 air conditioning split units where each split unit has local isolation in the form of a 20A rotary isolator. I didn't think twice about listing this as a defect, I was taught from day 1 that accessories must have a current rating equal to or greater than the design current of the circuit for obvious reasons. My supervisor has subsequently rubbished this claiming that due to there being fixed equipment connected to the load side of the isolator that does not run close to 20A that the problem is mitigated. Whilst I see his point I still don't think its right & have been looking in the regs for a definitive answer to the question, so far I've only found 512.1.2 under selection & erection...

512.1.2 Current
Every item of equipment shall be suitable for: (i) the design current, taking into account any capacitive and inductive effects, and (ii) the current likely to flow in abnormal conditions for such periods of time as are determined by the characteristics of the protective devices concerned.

Just wondering if anyone has any thoughts on this or can point me in the direction of a reg that categorically proves me or him right.

Thanks in advance!

Nick.

 

[Strima]

For a fixed load the design current would be that of the load not the protective device rating.

As there's no risk of overload I would see no issue and not code it.

 

[telectrix]

agree ^^^^^^. even if the circuit is running at full capacity of 32A, the isilator can't pass a current greater than it's load demand (except in the case of a fault condition in the load or it's connection cable ).

 

[Leezo]

agree ^^^^^^. even if the circuit is running at full capacity of 32A, the isilator can't pass a current greater than it's load demand (except in the case of a fault condition in the load or it's connection cable ).

But if there is a fault condition then the load could draw in excess of 20A, ie the rating of the isolator for a sustained amount of time while not pulling enough current to operate the 32A protective device thus potentially causing damage to the under rated isolator & therefore a fire hazard, seems like common sense to me?

 

[Strima]

Accessories are designed to take into account short duration fault conditions with no adverse effects.

 

[Leezo]

For a fixed load the design current would be that of the load not the protective device rating.

As there's no risk of overload I would see no issue and not code it.

But if there is a fault condition then the load could draw in excess of 20A, ie the rating of the isolator for a sustained amount of time while not pulling enough current to operate the 32A protective device thus potentially causing damage to the under rated isolator & therefore a fire hazard, seems like common sense to me?

 

[snowhead]

The 20a isolator will already be rated for overcurrent.

If there was sufficient current ot set fire to the Isolator the Air Con unit would probably already be on fire.

 

[Leezo]

The 20a isolator will already be rated for overcurrent.

If there was sufficient current ot set fire to the Isolator the Air Con unit would probably already be on fire.

Yes, rated for some overcurrent at 20A.

Have you never seen a circuit accessory that's overheated &/or melted over a period of time? I know I have.

 

[Julie.]

But if there is a fault condition then the load could draw in excess of 20A, ie the rating of the isolator for a sustained amount of time while not pulling enough current to operate the 32A protective device thus potentially causing damage to the under rated isolator & therefore a fire hazard, seems like common sense to me?

How could this "fault" condition occur?

- if it's a short circuit fault, then you design the protection, cable etc to give a Zs low enough to ensure the protective device trips quick enough - if this isn't the case, it's not an isolator issue it's a proactive device issue.

- If it's an overload condition (not a fault) , then the fixed load (such as a 4 ring hob, has to switch a 5th or 6th ring on in order for it to occur!! - so isn't possible), in the case of motors etc, there is a possibility of overload, but usually there is motor protection locally, such as the case with an air-con unit.

 

[Leezo]

How could this "fault" condition occur?

- if it's a short circuit fault, then you design the protection, cable etc to give a Zs low enough to ensure the protective device trips quick enough - if this isn't the case, it's not an isolator issue it's a proactive device issue.

- If it's an overload condition (not a fault) , then the fixed load (such as a 4 ring hob, has to switch a 5th or 6th ring on in order for it to occur!! - so isn't possible), in the case of motors etc, there is a possibility of overload, but usually there is motor protection locally, such as the case with an air-con unit.

I didn't design the cct Julie so none of that is down to me or part of the issue. Any number of faults could occur in an air con unit, its not just a motor.

 

[Julie.]

I didn't design the cct Julie so none of that is down to me or part of the issue. Any number of faults could occur in an air con unit, its not just a motor.

Agree, but if you are doing an EICR then you need to go over the design in terms of checking compatibility of the protective devices to the cable size, Zs etc.

Of course there could be many faults within the air-con unit, but unless you have the full diagram etc, you can't assess it. Are you doing an EICR on the electrical system or the inner workings of all electrical and electronic equipment on-site?

Air con units are designed with various protections internally for each area, electronics, motor, etc. you would really have to have all the details of the design in order to assess this!

 

[snowhead]

Have you never seen a circuit accessory that's overheated &/or melted over a period of time? I know I have.

Since the advent of plastic, self extinguishing, isolators / accessories, Yes, many times.
Moreso on circuits with a protective device that matches the Isolator rating, or even less, than those where it didn't.

You've reported your concerns, they've been dismissed, that's it as far as you're concerned.

 

[Leezo]

Agree, but if you are doing an EICR then you need to go over the design in terms of checking compatibility of the protective devices to the cable size, Zs etc.

Of course there could be many faults within the air-con unit, but unless you have the full diagram etc, you can't assess it. Are you doing an EICR on the electrical system or the inner workings of all electrical and electronic equipment on-site?

Air con units are designed with various protections internally for each area, electronics, motor, etc. you would really have to have all the details of the design in order to assess this!

Yes of course I'm assessing the compatibility of protection & wiring, there's no issue there, there is this issue of compatibility between cct protection & the rating of accessories. I agree there is built in protection with appliances like these but I'm a sparky & I'm not really concerned with that, just the suitability of the system taking into account a multitude of eventualities.

What I guess I'm really looking for is for someone to tell me where in the regs it says that a fixed load of a certain size negates the designers responsibility to select suitably rated accessories for the design current, then I'll wind my neck in if I'm wrong. I have to say though I don't agree with this statement made in the first reply to my post that in the case of fixed equipment the design current is that of the load of the appliance as any Tom, Dick or Harry can work on the load side of an isolator & change the A/C unit for one with a higher current rating.
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Since the advent of plastic, self extinguishing, isolators / accessories, Yes, many times.
Moreso on circuits with a protective device that matches the Isolator rating, or even less, than those where it didn't.

You've reported your concerns, they've been dismissed, that's it as far as you're concerned.

JOKER... quote where in the regs it backs up your 'opinion' before you try telling me that. I didn't come on here to "report my concerns" I came on here for the advice of people who know what they're talking about so enough from you.
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Accessories are designed to take into account short duration fault conditions with no adverse effects.

Yes, over & above that of the rating of the accessory which in this case is 20A, the problem is, the protective device is 32A so how long should I expect my isolator to cope with something close to 40A before it melts.

 

[Julie.]

Yes of course I'm assessing the compatibility of protection & wiring, there's no issue there, there is this issue of compatibility between cct protection & the rating of accessories. I agree there is built in protection with appliances like these but I'm a sparky & I'm not really concerned with that, just the suitability of the system taking into account a multitude of eventualities.

What I guess I'm really looking for is for someone to tell me where in the regs it says that a fixed load of a certain size negates the designers responsibility to select suitably rated accessories for the design current, then I'll wind my neck in if I'm wrong. I have to say though I don't agree with this statement made in the first reply to my post that in the case of fixed equipment the design current is that of the load of the appliance as any Tom, Dick or Harry can work on the load side of an isolator & change the A/C unit for one with a higher current rating.
[automerge]1584706146[/automerge]

JOKER... quote where in the regs it backs up your 'opinion' before you try telling me that. I didn't come on here to "report my concerns" I came on here for the advice of people who know what they're talking about so enough from you.

well 432.3 is the obvious one!

I think snowhead's comment is that you reported your concern to your supervisor, he has dismissed it therefore that's it.

 

[Leezo]

well 432.3 is the obvious one!

That's about protective devices, it certainly doesn't refer to selection of under rated accessories?