commando sockets

[scotsgraeme]

Hi,
I have a query regarding 16A 230v commando sockets.
I have been told these cannot be on a ring, and must be wired individualy as a radial from their own 16A MCB or RCBO. is this correct?
I am hoping to have two of these fitted adjacent to each other to supply power for a pair of immersion heater elements, which draw too much curent to go on a 13a socket. they need to be able to be unplugged, so using a FCU isn't an option.

 

[phatboy]

Hi,
I have a query regarding 16A 230v commando sockets.
I have been told these cannot be on a ring, and must be wired individualy as a radial from their own 16A MCB or RCBO. is this correct?
I am hoping to have two of these fitted adjacent to each other to supply power for a pair of immersion heater elements, which draw too much curent to go on a 13a socket. they need to be able to be unplugged, so using a FCU isn't an option.

Sounds right, as the commando plugs are not fused. You could connect them both to the same radial, but it would have to have a 16amp MCB or RCBO, which wouldnt be suitable for your needs

 

[plugwash]

The plugs have no fuses so they need appropriate overcurrent protection in the fixed wiring. I seem to remember reading somewhere that protective devices up to 20A was considered acceptable protection for 16A sockets but I don't recall where I read that and it doesn't really help you much since from what you say the total load of these will be above 20A anyway.

As I see it you have at least two choices.

Run two seperate 16A circuits from an existing CU/DB to seperate 16A socket.
Run a 32A circuit from an existing CU/DB and place a small CU next to the sockets with a pair of 16A breakers (one for each socket) to provide overcurrent protection. The small CU could also be used to provide RCD protection.

If the two immersion heaters are attatched to the same mobile object you might also want to consider a third option.

Run a 32A circuit to a 32A socket and then mount a small CU on the mobile object to provide overcurrent protection for the two heaters.

 

[Iggifer]

I seem to remember reading somewhere that protective devices up to 20A was considered acceptable protection for 16A sockets but I don't recall where I read that

I have seen lots of 16A commando sockets protected by 20a over current devices, in a brand new MG rcbo distribution board, would like to see where it says its ok though

 

[scotsgraeme]

cheers. i was just making sure i wasnt being given wrong info. the two circuits is a definite option, there will be a full house rewire happening at the same time so running an extra load of cable isn't a huge deal. running a 32a circuit to another CU isn't ideal as i doubt an extra big box on a wall will pass the WAF. the big blue sockets are pushing it as it is.

 

[plugwash]

Out of interest what is this for?

 

[Iggifer]

I was wondering what kind of immersion heater you would need to unplug as well

 

[RF Lighting]

I seem to remember reading somewhere that protective devices up to 20A was considered acceptable protection for 16A sockets but I don't recall where I read that

I have seen lots of 16A commando sockets protected by 20a over current devices, in a brand new MG rcbo distribution board, would like to see where it says its ok though

It's in the OSG pg160. Don't think it's specifically mentioned in BS7671, but neither is using 13A socket outlets on 20A circuits.

 

[Iggifer]

so it does. I knew I'd seen it somewhere.

 

[scotsgraeme]

Out of interest what is this for?

it's for brewing beer. a 100l pot with a pair of elements in. it's only portable when empty, moving 100l of hot water or hot wort is not a good plan.

 

[ericmark]

To ensure the rating of the socket is not exceeded you can either put a current operated disconnection device at the socket or at the supply.

At the supply would mean a cable for every socket and at the socket a single cable could supply many sockets.

This

is a 32A version but shows the idea of fitting a RCBO in the socket outlet so many sockets can be daisy chained from same supply.

As to using a ring circuit the calculations to ensure there is not an overload could become complex one can't use the 13A example and just use 16A it will need to be calculated. Can't see the point may as well just use 4mm or 6mm cable in first place.

I have with 110v supply used a 6mm ring supplying a series of 16A sockets all with 16A MCB's in the outlet and from a 32A MCB in the distribution unit but not because of current used but to reduce volt drop in a large workshop.

Appendix 15 does say you should not supply an immersion heater from the standard final ring circuit. I would think this is because the load is sustained for quite a long time and as such it would be easy to overload as other items were supplied from the same ring.

In general fixed appliances over 2kW should not be connected to the ring. If one was to go by the letter this would also include the washing machine, tumble drier, dish washer and oven. All should have a dedicated supply. However non of the other items draw power for a long as the immersion heater so although one may turn a blind eye to a washing machine plugged into the standard final ring circuit the immersion heater is never connected to the ring.

 

[shedbang]

it's for brewing beer. a 100l pot with a pair of elements in. it's only portable when empty, moving 100l of hot water or hot wort is not a good plan.

There is no finer reason for doing anything. We must help this man.

 

[scotsgraeme]

i think i'll have them installed on a 16A RCBO each, that way if somethin goes wrong they dont trip everything else.
the sockets are mostly an afterthought as far as the wiring goes, SWMBO would probably rather the rest of the house was concentrated on, although if i don't get brewing again soonish, i'll run out of beer.

 

[Taylortwocities]

Move south to Oxfordshire. The environment is ideal for brewing beer

and you'd get free sparky assistance too