commando sockets – Fuse ?

[46philh]

Command sockets – Fuse ?

I got several commando sockets put in the garage when we had the house rewired. Each one is connected to its own MCB. I am only intending to run kettle elements on them for the time being,

On a normal kettle lead the plug has a fuse but what happens with commando sockets ?

[Aleman]

IGNORE THIS - Complete brain fart on my part

You normally use them with a fused connection unit . . . Mine are switched as well.

I would have thought that a Pro electrician would have used the correct boxes, as its a violation of the 16/17th editions of the regs to not do so

[AnthonyUK]

A 13A fused spur is not much use on a 16 or 32A circuit.
A fuse is primarily there to protect the wiring from overloading and an MCB should do this.
What rating is your MCB?

[Pinto]

A 16A commando outlet is rated to run at the full load capacity of the circuit (16A) - no additional fusing is required as an overload will shut down the MCB without risking damage to the outlet or cabling. If you run a converter to 3 pin fly lead, additional fusing us provided at your 3 pin plug.

You can also buy combined Isolator/ commando outlets :



Or use a rotary 3 pole isolator in line - but that's isolation, not fusing - two very different things

[46philh]

Thanks for your help.

Yes I found out about those combine Isolator/ commando outlets later after the sparky has done all the work. Might upgrade to them in the future.

[Waffty]

For my 50L Braumeister, I have a 32A breaker in my main distribution board, I then feed a separate 'mini' distribution board in my garage that has an RCD and two 16A MCBs fitted, I then use the exact same 16A command/Isolation switch combo as above. I then use a heavy duty i.e 20A rated cable (un coiled) to my Braumeister. Works perfectly, it's over engineered for the purpose as I'm only planning to use the one 16A connection. Even after an extended boil period, there's no hint of the cable(s) getting warm.

[Fil]

fwiw you can ebay small single mcb consumer units, i have 2 x fitted in my shed on each of the 16a feeds i have fixed up, in theory these will trip localy before the 32a mcbs in the main consumer unit. so i should not need to march off all the way back to the house if a short should occur

[alix101]

You don't need to fuse the comando sockets the fuse protects the equipment not the circuit or the socket these are protected by the mcb/fuse in DB.
But you shouldn't plug in equipment which can't take 16A or 32A without additional in line protection after the socket also you need appropriate sized cable, you shouldn't be plugging anything less than 4mm cable into a 32A comando socket without additional protection or 2.5mm into a 16A.
Again if yor elements are only 2.2 kw then these need protecting.

[themadhippy]

the fuse protects the equipment

nope,the fuse is there to protect the cable

[Waffty]

As I understand it, a fuse is there to protect something, be it a device or be it a cable. Any fuse will blow at a set current and or for thermal fuses at a set temparature rating. In DC circuits, you can have milli amp quick blow fuses, to protect sensitive electronic circuits.

Agreed that in most house hold instances, the fuse board breakers are there to protect against an overload Ie X number of kettles on say a ring main or more often to protect against a fault such as a short circuit. In which case the main aim is to pop the fuse before the cable gets too hot and potentially causes a fire. Most houses have a 60A main fuse, some newer 100A fuse, this is then divided down to smaller fuses via your distribution board, typically 5A, 16A, 30A, 32A and 45A. All new boards should also have an RCD to protect against current leaking to earth ie a fault or a potential electric shock. Your typical 13A plug socket hangs off' a 30A breaker ring main and is then independently fused by the fuse in the plug top, typically 1A, 3A, 5A and 13A depending on current draw and cable rating.

So there are many ways to skin the cat but you must always have an RCD in line, metal and liquid don't mix. You should always have the correct cable rating especially when drawing a load for a prolonged period of time ie 90 minute boil for example and you should always make sure you have the correct fuse rating for the appliance and the cable you're using. Finally, make sure all your earths are present.

In my setup, I have a 60A main fuse, a 32A breaker and RCD in my distribution board. I then have 6mm cable to a 2 fuse and RCD mini dis board in my garage. I only use one fuse, which is 16A and I run 2.5mm cable to my 50l braumister. So at every point I'm protected. A fault, say a nail through my 6mm cable will pop my 32A breaker an possibly pop my RCD and a fault on my Braumister side could pop both RCDs or just the 16A breaker.

There's nothing stopping you using fixed fuses in say fused spur boxes, provide they are rated for the job and they have the correct fuse fitted Ie no point using a 13A rated fused spur, with a 16A fuse for a 15A load for 90 minutes as whilst it may work at first, it won't for long and could well go up in smoke.

If in doubt, speak to a professional, you're a long time dead and I'm sure no one wants the fire service to dump a 1,000 odd litres of water on your worldly possessions.

[orlando]

A naive question for you. Some of you may have seen my travails with standard hot leads shorting badly and melting. I have had a separate board installed in my brewery which I believe is 32A. My kettle and HLT have standard 2.4 kW elements (Lardy supplied). Do I have the option of using these kind of leads or are the deigned for things like big hot water tank style elements? I want my sparky to come round and sort the problem out for me but if there is a ready solution it will save me a few quid.

[Waffty]

Orlando,

Lets break this down.

So a 2400W element (assuming it is 2400W and no say 2450W, 2500W etc), then at 230V AC, you're looking at a current draw of 10.5A, a domestic 3 pin plug is capable of delivering 13A, so alls good? Well you'd think so but your average kettle takes say 5 minutes to boil, most people only take a shower for say 10 minutes. In fact, in the domestic home, few items actually draw high current for a prolonged period of time ie immersion heater, electric fire, electric cooker, then elements of a tumble dryer and washing machine, in fact, the only thing close to our requirements is a wall paper stripper and if you've ever owned/used one, you'll know you're only advised to us it for 30 minutes at a time and interestingly, the cable is very heavy duty.

Ok, so for your installation, if you have a confirmed 32A supply, then by splitting this into two 16A circuits (via a mini consumer unit) I would just go for two 16A commandos, wired with heavy duty 2.5mm flex cable, (check out the type of cable they use for camping/caravan mains hook ups, just make sure it 2.5mm). This will be bullet proof for your requirements. To back this up, an immersion heater element is typically 3000W and these literally run all day and night on a 16A breaker.

I personally would avoid plug tops, unless they are designed to run 13A loads all day long, in addition, I personally would only by Crabtree or MK electrical components.

I have run a 2750W element on a domestic plus by my installation was MK all through, my plug and element connectors were know 'hot' friendly and I was using 2.5mm cable + all backed off to the correct breakers and an RCD.

Good luck.

[alix101]

the fuse protects the equipment

nope,the fuse is there to protect the cable

Nope it protects both,the cable should be rated to suit the appliance as should the fuse, any appliance less than 750w should be protected by a 3A fuse and 13A up to 3kw . Take a boiler for instance this appliance should be correctly fused in the spur at 3A this isn't to protect solely the supply cable / flex which will be generally rated much higher but the appliance itself despite these having additional internal fuses.

[orlando]

Orlando,

Lets break this down.

So a 2400W element (assuming it is 2400W and no say 2450W, 2500W etc), then at 230V AC, you're looking at a current draw of 10.5A, a domestic 3 pin plug is capable of delivering 13A, so alls good? Well you'd think so but your average kettle takes say 5 minutes to boil, most people only take a shower for say 10 minutes. In fact, in the domestic home, few items actually draw high current for a prolonged period of time ie immersion heater, electric fire, electric cooker, then elements of a tumble dryer and washing machine, in fact, the only thing close to our requirements is a wall paper stripper and if you've ever owned/used one, you'll know you're only advised to us it for 30 minutes at a time and interestingly, the cable is very heavy duty.

Ok, so for your installation, if you have a confirmed 32A supply, then by splitting this into two 16A circuits (via a mini consumer unit) I would just go for two 16A commandos, wired with heavy duty 2.5mm flex cable, (check out the type of cable they use for camping/caravan mains hook ups, just make sure it 2.5mm). This will be bullet proof for your requirements. To back this up, an immersion heater element is typically 3000W and these literally run all day and night on a 16A breaker.

I personally would avoid plug tops, unless they are designed to run 13A loads all day long, in addition, I personally would only by Crabtree or MK electrical components.

I have run a 2750W element on a domestic plus by my installation was MK all through, my plug and element connectors were know 'hot' friendly and I was using 2.5mm cable + all backed off to the correct breakers and an RCD.

Good luck.

OK, so in short no, I have to use an immersion element, correct?

[Waffty]

The example of the immersion heater was to give a parallel between our brewing requirements and those of a domestic water heating installation ie if you follow the same principles then you won't have a problem.

So let's break this down. You already have a 32A supply from your distribution board, so ideally you need one of these or similar at the end of the 32A supply.

http://www.ebay.co.uk/itm/Caravan-Campi ... Sw~bFWJoC~

This would be perfect, as you get 2 dedicated 16A breakers a 40A RCD and two 16A commandos.

I would then go for something like this or be it shorter if you can find it, as this stuff will deliver 16A pretty much, all day long.

http://www.ebay.co.uk/itm/10M-2-5mm-sq- ... SwnDZT2SZh

Then all you need to do is wire the cable into your element, if it's the wire in type or wire it into a suitable hot rated 'kettle' type connector and this should be able to deliver your 2400W load pretty much for 24hrs a day. As you have 2x16A commandos on the above unit, just double up the setup for the other fuse/connector.

Appricate the above isn't cheap but in theory, it should last you a lifetime and you'll be safe in the knowledge that it's been spec'd for the job in hand. In addition if you ever wanted to step up to 3,000W elements, then the above config would also work or be it, I wouldn't recommend running them both for 24 hrs