Coding question - 8.5kw shower, B32

[Pretty Mouth]

How would you code this?

A 8kw shower (so pulling ~37A) is protected by a B32 breaker. 6mm² cable rated at 47A, ref method C
(Actually, that last bit isn't true. In fact it's currently ref 101 = 27A, but an easy fix to get it to ref C, so for the sake of the discussion, let's pretend it's ref C)

I'm torn between C2 and C3. I suspect it's technically a C2, but after at least several years like this (date on shower 2014, circuit installation date 1997), and with no apparent ill effect on any of the equipment, I find it difficult to sell it to the client as potentially dangerous.

 

[telectrix]

i calculate 33.3 A @ 240V - 35A @230V. code 3 IMO.

 

[Pretty Mouth]

i calculate 33.3 A @ 240V - 35A @230V. code 3 IMO.

Thanks Tel. Sorry, should have read 8.5kw. Too late to edit!

 

[loz2754]

I think C2 is more appropriate personally, as the circuit breaker is subjected to a sustained overload every time the shower is used and may eventually break down. Albeit the shower may be in use only for short periods.

 

[telectrix]

just get it to ref. C and bung in a 40A MCB. less hassle that giving it a C2 and having to go back to rectify.

 

[Deleted account]

I’d C3 that one personally.

 

[Wilko]

I think this is where inspection is so important. If there is no thermal damage after years of use then C3. The section in insulation more than 100mm deep is a good spot to look - move and replace if necessary.

 

[Pretty Mouth]

just get it to ref. C and bung in a 40A MCB. less hassle that giving it a C2 and having to go back to rectify.

Can't unfortunately. It's one of those old volex jobs that clamps to the busbar with the screw rather than the cage. I can't get one for love nor money.

 

[brianmoooore]

i calculate 33.3 A @ 240V - 35A @230V. code 3 IMO.

Did you mean it that way around? I can assure you that a fixed resistive load will draw more current on 240V than on 230V.
I'd stick a clamp meter on it before deciding any further.

 

[Pretty Mouth]

I think this is where inspection is so important. If there is no thermal damage after years of use then C3. The section in insulation more than 100mm deep is a good spot to look - move and replace if necessary.

I had a look at the cable under the insulation and it seemed fine, there was no visible signs of damage. Tested fine too. I'd bet money that there's nothing wrong with it.

I went to replace a shower a few months back, but ended up having to rewire the circuit. Again a 32A breaker, ref 101, but this time 4mm T+E with a 9.5kw shower! Out of curiosity I cut open the old cable where it had run under the insulation, to have a good look at it. You wouldn't be able to tell it from new, it seemed mint apart from it being old colours red/black.

 

[Pretty Mouth]

Did you mean it that way around? I can assure you that a fixed resistive load will draw more current on 240V than on 230V.
I'd stick a clamp meter on it before deciding any further.

I think what Tel meant is shower MI's usually give the shower rating for running at both 230V and 240V. I didn't specify which. Eg, Triton Aspirante 8.5kw shower would draw 8.5kw at 240v, or 7.8kw at 230v

 

[brianmoooore]

Nominal UK voltage is 230V, so if that's the shower in question, it's rated at 7.8kW, which equates to a shade under 34A, so not overloading a 32A MCB by any great amount. Still an overload though, so needs coding.

 

[telectrix]

the current is dependant on voltage and resistance as per ohms law. a 8.5kW shower wiill draw 35A at 240V to achieve the wattage. drop the volts to 230V and the kWs will be lower as the current drawn depends solely on the resisitance of the element and the voltage applied to same.

 

[e-spark]

check the cable condition at CU, isolator and shower if no signs of thermal damage and it tests ok replace with B40 MCB or RCBO if needed. id code it C3 if no damage and tested ok

 

[nicebutdim]

Not an opinion, but a question*

Some responses have mentioned that signs of thermal damage to cable (lack of in this case) would affect coding. What I can not help wondering is should the type of load be given consideration in this situation? What I'm getting at is the fact that the householder may take relatively showers in moderately warm water, but change of tennancy/ownership could see hotter showers, for much longer periods of time becoming the norm and could quickly and drastically change the physical condition of this circuit.

Should this be given consideration or does coding solely depend on what you find at time of inspection? Sorry for the interruption and please feel free to point out if this is simply daft.

 

[brianmoooore]

Running the shower hotter doesn't make it use more power; it just means the water flow rate is less.
That doesn't apply to longer showers, of course, but an EICR is a snapshot in time, just like your car's MOT test.
Doesn't stop you adding comments if you think something might deteriorate in the future.

 

[andyb]

I’m sure I’ve completely misunderstood this thread, and I’ve read through it a couple of times, but I have had a couple of scotches.

We’re saying that, and I’m taking everything written as correct, that we have a cable rated at 47a, protected by a 32a mcb and we’re looking to give it a code 2? Have I got this right?

The other way round I would understand, but what’s the problem?

 

[brianmoooore]

Cable is fine. The problem is that the load is slightly greater than 32A, so it's the (obsolete) MCB that is being queried.

 

[Pretty Mouth]

I’m sure I’ve completely misunderstood this thread, and I’ve read through it a couple of times, but I have had a couple of scotches.

We’re saying that, and I’m taking everything written as correct, that we have a cable rated at 47a, protected by a 32a mcb and we’re looking to give it a code 2? Have I got this right?

The other way round I would understand, but what’s the problem?

Not exactly. The cable is fine for the load, it's not a concern (or at least it won't be once i dig it out from the loft insulation).

The problem (or perhaps not) is that the breaker is rated lower than the load. Could, as @loz2754 suggests, repeated overload of the breaker over the long term cause damage to it that might result in danger?

I suspect not, but I don't know that for certain, hence the question

 

[andyb]

Well there's certainly a discussion to be had I suppose, but if we're talking about an EICR I don't see a problem, and I don't understand why you would look for damage to a cable being utilised below it's ccc.

Like I said, I've had a scotch, or 2, and I probably shouldn't be anywhere near a keyboard at the moment.

I'll have a look in the morning.