Checking electric supply for 20 amp capability - HOW ?

[KWMc]

Hello - hoping someone has done this before. I have an outside supply, in a garage, installed long before I came to this house, and without a clue as to it's capability. I need to check if it can supply 20 amps for an external sauna. How do I do it.

 

[ajrobb]

Turn off all the MCBs or remove all fuses that are rated below 20A. If the garage still works...

I don't know if OSG Appendix applies: "8.5 Water and space heating
Water heaters fitted to storage vessels in excess of 15 litres capacity, or permanently connected heating appliances forming part of a comprehensive space heating installation, should be supplied by their own separate circuit."

 

[holmslaw]

..

 

[stillp]

How do I do it.

Start by getting an electrician to carry out a PIR. As holmslaw has implied, there's more to this than the ability to supply 20A.

 

[plugwash]

by tracing where it is supplied from and then looking at the cable sizes, run lengths (important for volt drop), protective device ratings, existing loads etc.

You can then run through the design calculations as if you were designing from scratch and figure out whether it is suitable or not.

 

[Taylortwocities]

20amps for a sauna?
I think you'll have to wait a long time for that to get hot enough to make you sweat!

 

[SgtTrojan]

Turn off all the MCBs or remove all fuses that are rated below 20A. If the garage still works...

Odd.

You need to know what size the cable is (printed on cable sheath).
You need to know what size circuit protection it already has. (printed on the device or the colour of the dot on the fuse carrier)

This is only for starters.

 

[ajrobb]

Interesting position being taken by a lot of people here. Even if a circuit exists that is protected by a 20A fuse or more, it is not necessarily good enough for a 20A load. I suppose it is fair enough if you can't see the design and testing results documents.

Nowadays I get the impression that a supply to an outbuilding would come under Local Authority Building Control. It might be possible that the existing circuit was notified to LABC. If so, they should have a record of it. Would that make it acceptable?

Or is it that OSG Appendix 8.5 does apply?

 

[ericmark]

I would start with simple measure the earth loop impedance only a matter of plugging in meter does it pass. Since there will be more than the tub and you need to go by breaker sizes available needs to be lower than 1.44 ohms.

Next easy is cable size is it 4 mm sq or over?

Then what route does it go though? anything which will de-rate the cable?

But since a earth loop impedance meter is not often found in a DIY tool kit then really a case of get an electrician to check it for you.

 

[SgtTrojan]

The circuit isn't protected by a 20 A fuse otherwise, I would assume, the OP would just install what he needs without him being concerned.