shed sockets,lights and welder

manus30

hello there,
planning on wiring a shed with 4 double sockets, two 5 foot fluosrcents and one 2 foot fluorescent. i will also be running a smallish 150amp welder.
I am thinking of doing it the following way:

• fit 32 amp mcb in dis board in house supplied from main bus after 63A main switch
• from here run 4 square twin and earth out to shed.
• in the shed i am thinking of having 3 circuits. 4 square runs into a main switch. from here run 1.5 sq into 6amp mcb for lights.
• for sockets, run 2.5 sq from main switch into rcd and then 16amp mcb.
• last circuit will be for the welder. run 2.5sq into 20amp mcb and out to one of those blue round sockets to run welder. no rcd on the welder circuit, i heard they will keep tripping with one.

I am not an electrician but do have a bit of knowledge of electricity due to working as a maintenance technician with mechanical background. i know though that a little knowlege can be dangerous so i would appreciate advice from experts here.
thanks in advance, some very knowledgeable and helpful people here.

2011

I would go larger than 4 sq.
You should not put a 32A MCB on a 4 sq.

More info please:

1) What is the lenght of run from the board to the shed?
2) What rating is the welder in terms of VA?

last circuit will be for the welder. run 2.5sq into 20amp mcb and out to one of those blue round sockets to run welder. no rcd on the welder circuit, i heard they will keep tripping with one.

you are not permitted to connect a socket such as this without using an RCD.

Use an isolator instead of a socket for the welder to get around this.

manus30

thanks for reply. shed is 6 metres from board.
ps, could you explain what sort of isolator could i use in order to get around the rcd problem with the welder and where would i put it in the circuit.
thanks.

mazthespark

isolator should be placed in same location as you would put the blue socket. and remove the plug from the socket and then hardwire the welder into this. welder will no longer be portable tho. any suitably rated isolator will do a 32a should be plenty. if the welder needs to be portable the socket and rcd arrangment may be better.

manus30

thanks. is there a suitable spec rcd i could use specifically for running a welder?

mazthespark

im not certain but possibly one with a higher rating or a special application rcd would do the job. Alternatively you could mount a small board at the blue socket location and have the welder on its own rcd then would just have to reset it there if or when it trips. coming from the main board in shed to this mini one containing only the rcd or rcbo and then on to the blue socket

2011

shed is 6 metres from board.

OK this is a no brainer. Use at least a 10 square cable as it will cost you very little for a piece that length. Too big a cable will not be an issue ever. It will also give you extra capacity for future additions. Also it will reduce the dimming of lights while you weld. You may find that your fluosrcents will switch off or flicker when you draw a large current while welding. The 10 sq. will reduce this. You would be best off using an SWA.

i will also be running a smallish 150amp welder.

This means nothing as a welder is in effect a transformer. 150 amps is the current on the secondary side. At 10 volts this would only be 1.5 kVA but at 100 volts it would be 15 kVA. That is why you need to know the rating of the welder oin terms of kVA. When you know the rating you can work out the current drawn on the primary side i.e form the mains.

could you explain what sort of isolator could i use in order to get around the rcd problem with the welder

Simple. Dont use a plug/socket connection on the welder. Have it permanently connected via a local isolator. Then is does not require an RCD.

where would i put it in the circuit.
thanks.

isolator should be placed in same location as you would put the blue socket.

+ 1

im not certain but possibly one with a higher rating or a special application rcd would do the job.

An RCD must be 30mA at a minimum for a socket circuit.

Do it like this:

Main board:

1) Install a 40 switch fuse not connected through any RCD. Connect a 10 sq. SWA to it.

2) Install a small distribution board in the shed. I like to use IP rated boards for this. Gland all of the cables into the bottom of the board.

3) Have a 63A main isolation switch in the board.

4) Install an 16A RCBO for all sockets in the shed. Wire sockets in 2.5. Use NYMJ, steel conduit or SWA for sockets. Not T & E.

5) Install a 6 or 10A MCB for all lighting. Use 1.5 NYMJ, steel conduit or SWA for the lights. Not T & E. I like to use IP rated plastic switches (like the MK ones) for sheds. This reduces shock risk with wet hands.

6) Install a suitable MCB for the welder isolator. This will depend on the welder size. Use a 4 sq. at a minimum, again depending on the load size. Use NYMJ, steel conduit or SWA for the welder isoltor.

7) ensure that the SWA armour and steel conduit is connected properly to earth.

Good luck!

manus30

top class info lads, thanks

indie armada

can i suggest using corrosion proof flouresent fittings, as opposed to the open batten type. there a little bit more exspensive but should get longer out of the bulb and the gear. i think a 58watt 5 foot single is about 22 euro+ vat or the higher output t5 are available in corrosion proof too.

HighlyCooL

just my tupence worth,

I have my shed wired with 6 twin sockets and a 16amp socket on a ring circuit wired in 2.5 back to a 20amp RCBO, 4 58watt twin vapor and gas proof fittings. wired back to the board in 1.5 with a 10amp MCB, garage door motor on a 16amp mcb, wired in 2.5 spured at the end.

all the drops down the wall and in steel conji and all the boxes are metal clad ones, the fuse board is a small plastic one.

feed form the house is about 12-15mts and is done in 10sq swa in ducting.

would have got a way with 6sq, but im glad i went with the 10, just leaves room for expansioon and that!


I have a small welder, with a 13amp plug top, have used in several times and no once triped the RCD!
i dont get why people think welders draw massive amounts of current, there the same as a yellow traffo in theory!

2011

i dont get why people think welders draw massive amounts of current, there the same as a yellow traffo in theory!

Large electric arc welders draw a large current, small ones draw a small current. The advice here is to establish the size of the welder so that the correct size cable could be selected. Welders by their nature have a high leakage current to earth, this can cause RCDs to operate. This will apply less to small welders such as yours.

HighlyCooL

yeah true, my small welder(130amp MMA/stick welder) with a normal plug top on the end never triped a rcd ones. having said that my traffo has a few times. most big welders would be 3ph. that ive seen any way. but best bet is to size it up. but if its on a normal plug top i would say not to worry about it if it trips it trips. or you could just put two circuits in on two rcbos. therefor if it does trip not all your loads are droped

2011

but if its on a normal plug top i would say not to worry about it if it trips it trips. or you could just put two circuits in on two rcbos. therefor if it does trip not all your loads are droped

+1

Bruthal

I have never really seen welders trip RCD`s, what they do trip is standard MCB`s because of the transformer start current at switch on and sometimes when striking the arc. Motor rated MCB`s through an rcd in shed and thats usually it sorted.

M cebee

have to agree

not aware of these problems with welding sockets

d type mcb and plenty big cable for VD and loop impedance