Domestic: 20A DP switches and ring final circuits??

[8yf13l0]

Hi all .

Seeing alot of cases where I have seen 20A DP switches in a kitchen (for example) each feeding a radial 2.5t&e to each white goods appilance or similar, and the 20A DP switch primarys are fed from the 32A kitchen ring final circuits - Is this accepteble to BS7671?

I'm guessing if it's only serving a 1 gang s/o or 13A fused spur it would not be at risk of overload at the switch?

Please advise.

Many Regards

Jamie

 

[davesparks]

They are switching spurs, not radials.
Technically it is acceptable under bs7671
My personal opinion based on what I was taught as an apprentice is that it is wrong. But thankfully we cannot judge an installation based on personal opinion

 

[Flanders]

If it is supplying a 13 amp socket the yes it fine the 20 amp switch it just for remote switching but if the 20amp switch goes to a flex outlet then no as there is no overcurrent protection for the cable suppling the apliance

 

[HappyHippyDad]

Like the others have said if each spur is just feeding one appliance then this is deemed OK with BS7671 (See Appendix 15, BS7671). Although it doesn't actually show a DP switch it shows a FCU suppplying the fixed equipment so possible this isn't in line with BS7671 as there is no fusing down for the flex to the appliance as with all other scenarios shown in Appendix 15?

 

[Leesparkykent]

Like the others have said if each spur is just feeding one appliance then this is deemed OK with BS7671 (See Appendix 15, BS7671). Although it doesn't actually show a DP switch it shows a FCU suppplying the fixed equipment so possible this isn't in line with BS7671 as there is no fusing down for the flex to the appliance as with all other scenarios shown in Appendix 15?

The fuse will be in the plug top for the appliance.

 

[HappyHippyDad]

The fuse will be in the plug top for the appliance.

That would be the usual scenario Lee, but the OP just states DP switch going to appliance so I thought he meant straight to the appliance with no socket! He probably didn't mean that, as rereading that would not comply with BS7671, but it would be good to know if it was that?

 

[Dave OCD]

Personally I'd rather use a switched/fused spur and run the feed to it as a spur from a nearby socket on the local RFC, connecting 3x 2.5 T&Es neatly in a single 25mm metal box can be a pain.

 

[Paul.M]

Hi all .

Seeing alot of cases where I have seen 20A DP switches in a kitchen (for example) each feeding a radial 2.5t&e to each white goods appilance or similar, and the 20A DP switch primarys are fed from the 32A kitchen ring final circuits - Is this accepteble to BS7671?

Kitchen white goods such as washing machines, dish washers, under sink water heaters etc. Have a read of 554.3 - 554.3.3

It's also the way the manufacturers are asking for the neutral to be switched off locally for service and repair to safe gaurd against Neutral shocks.

 

[NDG Elecs]

I often use 20A DP switches for oven ccts these days, with any fusing down as necessary. I give the option of a 'proper' 32A cooker cct but many customers are happy with less. A lot of ovens don't pull much nowadays.

 

[sparkzalot]

Assuming they supply 1 socket. Fine. They are just switching spur. Supplying more than 1. No

 

[LankyWill]

A 4 gang grid style bank of 20a dp switches is a far neater and modern way of isolating appliances. Use a shaver box for ease of connection. Appliances can be fused down via a plug or a un-sw fused outlet.

 

[Dave OCD]

I wonder if the OP was questioning whether connecting the RFC conductors together in the feed side of a 20 amp rated switch could in itself cause an issue as on occasions there could be 30 amps + on those terminals ?

 

[Paul.M]

I wonder if the OP was questioning whether connecting the RFC conductors together in the feed side of a 20 amp rated switch could in itself cause an issue as on occasions there could be 30 amps + on those terminals ?

Someone please correct me if I am wrong:-

The 20A rating of a FCU is for the contacts within the switch and not the incoming terminals?

 

[Dave OCD]

I would have thought so Paul.

 

[Flanders]

I agree the terminal should be able to take load as they are the same size as sockets and spurs and anyway the terminal will never run at 32amps as the ring circuit is distributed in 2 directions

 

[Dave OCD]

Someone please correct me if I am wrong:-

The 20A rating of a FCU is for the contacts within the switch and not the incoming terminals?

Actually you mean a 20A DP switch as the rating of a FCU is usually 13 amps ?

 

[Dave OCD]

I agree the terminal should be able to take load as they are the same size as sockets and spurs and anyway the terminal will never run at 32amps as the ring circuit is distributed in 2 directions

Are you sure about that, I can't see how the current would differ appreciably throughout the circuit ?

 

[Paul.M]

I would have thought so Paul.

Yes I know, just wanted to "ask" instead of "inform" via a sarcastic format (I'm in that mood tonight). Very good point Dave btw.

Any switch rating is the amount of Amps it can take under normal usage without the contacts over heating/meting/burning via conducting electricity from the main supply to the load.

eg. A 6A light switch on a 10A MCB with a load of 8A.

Q. What do people think will happen in time?

 

[DPG]

Yes I know, just wanted to "ask" instead of "inform" via a sarcastic format (I'm in that mood tonight). Very good point Dave btw.

Any switch rating is the amount of Amps it can take under normal usage without the contacts over heating/meting/burning via conducting electricity from the main supply to the load.

eg. A 6A light switch on a 10A MCB with a load of 8A.

Q. What do people think will happen in time?

Being picky here, but you are saying the load on the 10A MCB is 8A. So that's OK. The 6A light switch will be OK, assuming the load it is switching is less than 10A. But I do get what you were intending to ask Daz

 

[Paul.M]

Being picky here, but you are saying the load on the 10A MCB is 8A. So that's OK. The 6A light switch will be OK, assuming the load it is switching is less than 10A. But I do get what you were intending to ask Daz

An 8A load protected by a 10A MCB is absolutely fine. The problem is with an 8A load conducting via a 6A rated switch! The contacts within the switch are over loaded and will quickly get warm then melt or fuse.

The OP's question about the 20A rating of a FCU, the 20A bit is for the load side and not the incoming terminals of the FCU.

 

[DPG]

An 8A load protected by a 10A MCB is absolutely fine. The problem is with an 8A load conducting via a 6A rated switch! The contacts within the switch are over loaded and will quickly get warm then melt or fuse.

The OP's question about the 20A rating of a FCU, the 20A bit is for the load side and not the incoming terminals of the FCU.

Ha ha, I was being picky with the way the question was worded. Not to worry. Daz

 

[telectrix]

Yes I know, just wanted to "ask" instead of "inform" via a sarcastic format (I'm in that mood tonight). Very good point Dave btw.

Any switch rating is the amount of Amps it can take under normal usage without the contacts over heating/meting/burning via conducting electricity from the main supply to the load.

eg. A 6A light switch on a 10A MCB with a load of 8A.

Q. What do people think will happen in time?

the light will go out.

 

[DPG]

But the switch will start emitting light instead Daz

 

[Paul.M]

Ha ha, I was being picky with the way the question was worded. Not to worry. Daz

It's been fun

the light will go out.

unless the contacts are fused?? (had that problem once on a dimmer switch were the winding's just fused together)

But the switch will start emitting light instead Daz

That is a safety feature, glowing switch so you can see where to turn the lights on before walking into a dark room and stub your toe on the coffee table leg! :rofl: done this, my little toe hurt for 3 days!

 

[Lucien Nunes]

OK, so we have a 20A DP control switch with its supply side as a point in an RFC protected at 32A. The load side connects to some accessory, either a single socket outlet or FCU, that will limit the load to 13A by way of the BS1362 fuse. We declare it as a fixed load so the 20A switch is within its thermal (continuous load) rating.

But what happens with a short circuit on the unfused spur? The 20A switch has to survive the fault being cleared by a 32A device without disintegrating, instead of a 20A device. Any accessory intended for use on an RFC will have been designed for that duty, but has the 20A switch? Check with manufacturers? Splitting hairs? Take it one stage further - given suitable cable would it be acceptable to control a 1A fixed load on a 40A circuit, using a bog standard 5AX light switch?

Discuss...

 

[Dave OCD]

OK, so we have a 20A DP control switch with its supply side as a point in an RFC protected at 32A. The load side connects to some accessory, either a single socket outlet or FCU, that will limit the load to 13A by way of the BS1362 fuse. We declare it as a fixed load so the 20A switch is within its thermal (continuous load) rating.

But what happens with a short circuit on the unfused spur? The 20A switch has to survive the fault being cleared by a 32A device without disintegrating, instead of a 20A device. Any accessory intended for use on an RFC will have been designed for that duty, but has the 20A switch? Check with manufacturers? Splitting hairs? Take it one stage further - given suitable cable would it be acceptable to control a 1A fixed load on a 40A circuit, using a bog standard 5AX light switch?

Discuss...

No because you'd never get the incoming 40a rated cable into the switch terminal.

 

[Dave OCD]

the light will go out.

Or stay on when the contacts have fused together.:smilewinkgrin:

 

[Lucien Nunes]

you'd never get the incoming 40a rated cable into the switch terminal.

I chose 40A for this very reason - Bare 2H2.5 MI will do 40A and will fit any decent light switch terminal. Anyway, does the cable need to be rated for 40A inside a panel and carrying a fixed load of 1A?

 

[Dave OCD]

Well let's say a 1mm cable was connected to the outgoing side of this switch feeding a 1 amp load, if there was a short in this section of the circuit the 40a MCB would still disconnect before any other damage was sustained ?

 

[rustynails]

I've done this sort of setup before but always put the fuse module before the dp switch