20 Double Pole switches

[pegasus]

I have a 30 A ring circuit and wish to install a 20A double pole switch on the ring to feed a single socket.

( The 20A double pole switch will be above a work top and the socket will feed a washing machine )

I am assuming this arrangement is ok. I have never seen it in print or DIY books. The suggestion is normally a Fused Connection Unit feeding a socket(s) or flex outlet socket.

Although I appreciate the 20 A value refers to the outgoing circuit, there is a possibility the cables on the ring side could be "carrying" 30 A.

This makes me wonder whether there is a maximum current for these terminals?

Is it the case that if you can get the cables in the terminal housing, there will not be an issue?

For example, could you install a 13A Fused Connection unit on a 40A radial circuit?

 

[Desie]

As you indicated the rating refers to the load not the supply. The amp rating therefore is almost irrelevent to the rating of the circuitg it sits on.

Example - all of your circuits come potentially from a consumer un it rated at 100A. The MCB then protects the individual circuits to prevent overload above their rating. i.e. a 40A circuit load is potentially 9200watts of power or 9.2Kw. A practical example of this is a large load electric shower.
You could potentailly take a 13A spur from this 40A circuit by installing a 13A FCU as you said.

The restrictor is really the load on the accessory side of the circuit being compatibke for the FCU and the size of the cable into the FCU or isolator its-self. I doubt you would get for example a 16mm cable into a 13A FCU.

By the way why would you want a 20A isolator for a washing machine? Is it an industrial one?

 

[JohnD]

I am assuming this arrangement is ok.

Yes, it is a splendid way to do it. An unswitched single socket under the worktop will reduce the temptation for anyone to plug in two large appliances.

 

[pegasus]

Thanks for speedy responses

The washing machine is standard ( at 10 A)

I went for a 20 A rating as they seemed to be the most commonly stocked.

From your replies, it is now clear that I could go down to a lower rating.

 

[Spark123]

You should not go for one rated less than for example a 13A FCU, whats to say in a couple of years you don't replace your washer for one which requires a 13A supply? 20A is fine. BTW did you know what you are doing is notifiable to your LABC if you are in England/Wales?

 

[securespark]

As you indicated the rating refers to the load not the supply. The amp rating therefore is almost irrelevent to the rating of the circuitg it sits on.

Example - all of your circuits come potentially from a consumer un it rated at 100A. The MCB then protects the individual circuits to prevent overload above their rating. i.e. a 40A circuit load is potentially 9200watts of power or 9.2Kw. A practical example of this is a large load electric shower.
You could potentailly take a 13A spur from this 40A circuit by installing a 13A FCU as you said.

The restrictor is really the load on the accessory side of the circuit being compatibke for the FCU and the size of the cable into the FCU or isolator its-self. I doubt you would get for example a 16mm cable into a 13A FCU.

By the way why would you want a 20A isolator for a washing machine? Is it an industrial one?

Just to clarify: if you attach a small load to a larger radial circuit, you need to make sure the cable to that load is rated to suit the protective device at the CU.

2nd point: not that we are mentioning immersion heaters here, but the OSG prohibits circuits supplying IH's having any other load attached to them.