Garage CU

[Electrifying]

But we're not talking about putting 32A down a 6mm cable, are we.

The 32A is the device protecting the cable - the design current is roughly 22A - the sum of the two MCBs in the garage CU - and that is the most that the circuit will be able to draw, so the volt drop will be lower.(and that's if the lighting circuit pulled it's full 6A, which is also unlikely.

This whole discussion came about because someone moaned about the 16A MCB that is currently installed not allowing discrimination with the 16A MCB in the garage - so I offer a solution and get picked to bits.

There was nothing wrong with my suggestion, unless you start thinking of extreme circumstances, and there's even less wrong with it now the OP has given us more detail

 

[ban-all-sheds]

We are talking about the capacity of the cable.

Its BS 7671 compliant capacity, if more than 29.5m long, is less than 32A.

 

[Electrifying]

We are talking about the capacity of the cable.

Its BS 7671 compliant capacity, if more than 29.5m long, is less than 32A.

I'm not following your thinking - can we have a Reg number or page please

 

[ban-all-sheds]

525.

 

[Electrifying]

525.

Okay, I've just read 525, I understand volt drop, so where are you getting your 29.5m?

 

[Steve]

525.

Okay, I've just read 525, I understand volt drop, so where are you getting your 29.5m?

Perhaps he worked it out!

Im bored of you now. You shouldnt have suggested to the OP that he replace his B16 with a B32. Thats that.

 

[Electrifying]

525.

Okay, I've just read 525, I understand volt drop, so where are you getting your 29.5m?

Perhaps he worked it out!

Im bored of you now. You shouldnt have suggested to the OP that he replace his B16 with a B32. Thats that.

If he's worked it out, he's worked it out wrong!

If you're bored, go read something else.

And as for telling me what I should or shouldn't do - please don't.
I hate people who think that they run a forum and that everyone should hang on their every word.
Hate having your statements questioned, don't you?

 

[Electrifying]

When you read this....

I would like some advice please.
Ive been asked to change a garage cu which has rewireable fuses. The garage has a 3 core 6mm swa cable coming from the cu in the house and is connected to 16a mcb. The cable has a gland fitting at cu in the house but has not got gland fitting at cu in the garage, would it be ok to fit this.

http://www.screwfix.com/prods/33248...nits/MK-Sentry-4-Way-RCD-Garage-Consumer-Unit

this...

The 3 core wires of the swa are connected to the rcd protected side of the cu, but theres no earth wire connected to the banjo on the gland fitting. The cable is burried and I would say the cable is no more than 20ft in lenght. Both the house and garage cu's are virtually in line with each other.

and then this....

Hi WOH64DEK,

Swap the 16A MCB for a 32A MCB.

If the circuit is on the RCD side of the house CU, then no need for RCD protection at the garage - buy a CU with an ordinary main switch.

If it's not RCD protected at the house, then you'll need RCD protection in the garage (like the CU in your link) - the distribution cable doesn't need RCD protection if it's SWA all the way.

Don't forget, full set of tests, EIC issued and it's notifiable work

If you don't feel competent or you don't want to pay to notify, get a sparky in, mate.

Good luck.

It turns out I was right, doesn't it

 

[Steve]

Congratulations on your victory. It clearly means so much to you. However your advice was given blindly. This is very foolish and I and RF Lighting were right to be concerned about this.

 

[ban-all-sheds]

If he's worked it out, he's worked it out wrong!

32 x 0.0073 x 29.5 = ..................?

 

[Electrifying]

If he's worked it out, he's worked it out wrong!

32 x 0.0073 x 29.5 = ..................?

6.89 V = 2.99%

That's all very well - for someone elses circuit

Ours is:

Design current - 22A

Volt Drop (3-core SWA) - 0.0064

Allowable volt drop - 5% = 11.5V

So,

22 x 0.0064 x ........ = 11.5

Answer: 81.67 meters

 

[ColJack]

It turns out I was right, doesn't it

no it doesn't.

you advised someone to alter the CPD for a cable which presumably had been designed by the installer for whatever reason without being there to see the circumstances of the installation.

 

[Electrifying]

It turns out I was right, doesn't it

no it doesn't.

you advised someone to alter the CPD for a cable which presumably had been designed by the installer for whatever reason without being there to see the circumstances of the installation.

Okay, if you want to be pedantic, it turns out my advice was right, not me

I was wrong to advise that a 6mm SWA cable could possibly be protected by a 32A MCB, before finding out if someone had run it through the loft on the way to the garage - okay

 

[ban-all-sheds]

6.89 V = 2.99%

That's all very well - for someone elses circuit

It applies to any circuit, assuming (which seems reasonable) that there's lighting on it.

Ours is:

Design current - 22A

Volt Drop (3-core SWA) - 0.0064

Allowable volt drop - 5% = 11.5V

So,

22 x 0.0064 x ........ = 11.5

Answer: 81.67 meters

But I'm not talking about that - I am answering your request here:

you present me with a genuine scenario where the current carrying capacity of our 6mm conductor, from house to garage, drops below 32A.

When it's more than 29.5m long.

Could you also provide figures and references to support your argument.

32 x 0.0073 x 29.5 = 6.9.

 

[Chri5]

20 amp would be fine