Appliance isolator switches

[JohnHarrison]

Do these have to be double pole? One idea is to run a large cable to a small sub CU in a kitchen cupboard and have an MCB for each appliance. This will not be DP of course.

 

[Taylortwocities]

They can be SP or DP unless the manufacturer specifies that both line and neutral must be isolated (boiler circuits e.g.).

Note that, generally, there is no requirement at all for there to be an isolator for kitchen appliances.

 

[JohnHarrison]

Thx. An oven needs one? yes? Local?

The idea is to have the oven, fridge, w/m, d/w and boiler on their own circuits. The boiler can have a simple local DP isolator at the boiler. The cooker hood and extractor can be off the ring.

 

[Taylortwocities]

Thx. An oven needs one? yes? Local?

No it does not. It may be a 'nice to have', but there is no regulation in BS7671 thast says there must be one.

 

[ericmark]

If your supply is TT then there may be, and only may be a good reason for double pole. But the double pole isolator allows you to find earth faults easier where many items are on the same RCD that is the main advantage. Using RCBO's in a kitchen consumer unit even if single pole get's rid of any need for double pole isolation (Unless TT). Using a master RCD and MCB's does mean for fault finding you have to go into some were to disconnect neutral for testing, but I have RCD feeding MCB's and it has been rare for faulty items not to show themselves quickly without having to disconnect them from neutral.

Safety wise there is no need to have double pole, OK with TT the RCD has to be double pole and main house isolator needs to be double pole but after that double pole only makes fault testing easy.

 

[JohnHarrison]

If not TT, you are saying have SP RCBO's in the kitchen CU?

 

[ban-all-sheds]

I being the person responsible for the design, construction, inspection & testing of the electrical installation (as indicated by my signature below), particulars of which are described above, having exercised reasonable skill and care when carrying out the design, construction, inspection & testing hereby CERTIFY that the said work for which I have been responsible is to the best of my knowledge and belief in accordance with BS 7671:2008, amended to 2015 except for the departures, if any, detailed as follows:

Somehow I don't think your signature on that would be valid - please get an electrician.

 

[ericmark]

If not TT, you are saying have SP RCBO's in the kitchen CU?

Yes

537.2.1 General
537.2.1.1 Every circuit shall be capable of being isolated from each of the live supply conductors. In a TN-S or TN-C-S system, it is not necessary to isolate or switch the neutral conductor where it is regarded as being reliable connected to Earth by a suitably low impedance.
Provision may be made for isolation of a group of circuits by a common means. if the service conditions allow this.

The exception is caravan and boat where even with a TN-S supply you need to switch the neutral.

 

[ericmark]

This does question the use of single pole MCB's or RCBO's in any consumer unit with a TT supply. In the main in the UK we tend to use a 100 mA RCD feeding consumer unit then 30 mA RCD's or RCBO's in the consumer unit, but that would mean the single pole devices are not forming new circuits. This would mean it does not comply with 314.1 unless twin pole MCB's or RCBO's are used. I have seen twin pole single width RCBO's but they only monitor overload current on the line not neutral where with double width it monitors neutral as well.

I have not seen any single width MCB's which switch line and neutral. Neither have I seen any consumer units on UK market which will take double pole MCB's. In Europe yes, but not in UK. I know when I wanted a distribution unit for 110 volt I had a problem locating a double pole unit and ended up using a three phase box leaving every third blank. They are clearly made in Europe you see them all the time, but rare in the UK.

So question to those who feel they can sign
I being the person responsible for the design, construction, inspection & testing of the electrical installation
If wiring a TT would they use a non type tested distribution unit to be able to use double pole? Or use a consumer unit and single pole? Or import a consumer unit from Europe?

 

[JohnW2]

This does question the use of single pole MCB's or RCBO's in any consumer unit with a TT supply. In the main in the UK we tend to use a 100 mA RCD feeding consumer unit then 30 mA RCD's or RCBO's in the consumer unit, but that would mean the single pole devices are not forming new circuits.

There is usually no problem if (as is commonly the case these days) all final circuits are protected by RCDs and/or RCBOs in the CU, since one then doesn't need the 'up front' RCD which causes all the problems.

Kind Regards, John

 

[winston1]

Thx. An oven needs one? yes? Local?

The idea is to have the oven, fridge, w/m, d/w and boiler on their own circuits. The boiler can have a simple local DP isolator at the boiler. The cooker hood and extractor can be off the ring.

As can the fridge, w/m, and d/w.

 

[JohnHarrison]

Thx. An oven needs one? yes? Local?

The idea is to have the oven, fridge, w/m, d/w and boiler on their own circuits. The boiler can have a simple local DP isolator at the boiler. The cooker hood and extractor can be off the ring.

As can the fridge, w/m, and d/w.

Want RCBOs on all circuits. If one appliance has a fault it does not cut out the others as is the case with an RCD.

 

[ban-all-sheds]

Want RCBOs on all circuits. If one appliance has a fault it does not cut out the others as is the case with an RCD.

How often have you experienced such faults with your appliances?

 

[JohnHarrison]

Want RCBOs on all circuits. If one appliance has a fault it does not cut out the others as is the case with an RCD.

How often have you experienced such faults with your appliances?

In case. Isolation and individual protection

 

[ban-all-sheds]

Multiple circuits, one per appliance, "in case" is bonkers.

What experience do you have of faults which make it seem like a good idea?