Voltage drop. Would you be concerned?

[DaveS79]

If you have calculated 4.7% I would be guessing you are using 240v as your nominal volatge?

Think you should use 230V?

But even so...

Have you even considered what current would be compliant over 25m+7m 4.0mm..   ( + whatever few metres you also have on your final circuits?)

Even a 20A MCB is just on the 3% limit..

NOW..   if you tell your customer you are only doing a 16A outbuilding supply.....

BUT if you really want a 32A supply....

Have you actually done calc's for 6.0mm over 32m?

Technically I think you will find that is just over 3% when calc'd using either 230v or 240v...

How big is the outbuilding?

How long will the final circuits in there be?

Guinness   

Thanks SL your correct I did enter 240 for nominal voltage and at 32 metres this does still come out over 3%. The ring could be as much as 40 metres in total and lighting 10 metres. I realise it's the total drop from furthest point of circuit to origin of supply that needs to meet voltage drop regs? so looks like will be quite way over if still go with 6mm and 32 amp supply. The outbuilding will be mainly used for t.v computer stuff and possibly washing machine and he had mentioned using power tools down there. What is your general approach for jobs that sound like this? Surely it isn't that common to run 10mm. Would you be more inclined to put it on 20 amps at supply and have 16 amp radials in the outhouse? Cheers

 

[binky]

power tools don;t tend to that energy demanding, and it's unlikely that they will be in use whilst watchingTV etc etc.  I think frm what you are saying you need to tell customer to stop being a tight fisted wazzock and go buy bigger cable, or suffer the consequences of a 16A supply, as that is all that regs will allow. I never did like customers who want to buy materials, they nearly always firk it up and make life difficult, and tend to be tight fisted idiots. You could also run 2 lengths of 4mm, giving equivalent of 8mm -  save the customer throwing away what he has already bought. 

 

[Andy™]

You could also run 2 lengths of 4mm, giving equivalent of 8mm -  save the customer throwing away what he has already bought. 

you could, but wh would you? customer got it wrong, they can pay to put it right. see how much its really saved them trying to do it cheap

 

[binky]

you could, but wh would you? customer got it wrong, they can pay to put it right. see how much its really saved them trying to do it cheap

well, that's a different question. Persoanlly I probably wouldn't have taken the job on in the first place as I can't stand customers who pee about buying things like cable. 

 

[tomsw18]

If you have calculated 4.7% I would be guessing you are using 240v as your nominal volatge?

Think you should use 230V?

But even so...

Have you even considered what current would be compliant over 25m+7m 4.0mm..   ( + whatever few metres you also have on your final circuits?)

Even a 20A MCB is just on the 3% limit..

NOW..   if you tell your customer you are only doing a 16A outbuilding supply.....

BUT if you really want a 32A supply....

Have you actually done calc's for 6.0mm over 32m?

Technically I think you will find that is just over 3% when calc'd using either 230v or 240v...

How big is the outbuilding?

How long will the final circuits in there be?

Guinness   

I checked a client's property the other week and he was getting 249V in to the Consumer Unit! 

Hi all

I have a job to supply a new 2 way board in outhouse. Am planning on running it from a 32 Amp MCB in 4mm twin and earth to adaptable box to outside and then 4mm SWA from there. The twin and earth is 7 metres and the SWA about 25 metres. My calcs for voltage drop comes in at  4.7% but this is at the full load of the 32 amp MCB. Obviousky 4.7% is higher than the 3% stipulated for lighting. Would others be concerned about this and increase cable to 6mm. Thanks

Given that this is a single short run, I don't see why you wouldn't go up to 6mm as the cost isn't that different. 

Either that or suggest a smaller protection device as they're unlikely to pull anywhere near 32A anyway.

 

[Evans Electric]

Either that or suggest a smaller protection device as they're unlikely to pull anywhere near 32A anyway.

Thats what I was thinking .     32A   is a lot of current in an outhouse ,   sounds over designed to me .          I've seen overkill  with 16mm cable to a shed with a light & a plug for the mower. 

 

[Andy™]

I checked a client's property the other week and he was getting 249V in to the Consumer Unit!

well within tolerance

 

[tomsw18]

well within tolerance

I know, but I was still surprised.