Outbuilding Supply lookover

[claret73]

Will start by apologising if this is long winded. I subcontract as a Mate & don't normally do my own work, yet have been asked to look at tidying up a supply to an outbuilding. Would like some clarification on what I've done & if I'm right? Or where I've gone wrong...

The outbuilding is currently used as a Bicycle Frame Spray Booth & Garage. He does Braze the odd Bicycle Frame in here too with Gas Flame Torch. From the House he has what looks to be 2.5mm SWA wired into some kind of plug in adaptor to a Socket Outlet. Runs 50-60m to the RCD Board in the Outbuilding. Causing nuisance tripping I believe or could be taking out the RCD on the Board in the House.

At the House end:

Main CU is a Push Fuse Type, no RCD. Incoming Supply Fuse marked up as 60A

Split off this is a MEM Fuse running to a Sub board in the Kitchen Extension, 16th Ed all ways have 30mA RCD Protection.

All Tails at Main CU & Henley Blocks look to be 25mm & 16mm Earthing Conductor.

There are spare ways on the Sub Board but I have no means of splitting the supply there to give me Sole RCD Protection for the outbuilding without affecting the circuits in the extension.

At the Outbuilding:

2.2KW Air Compressor

1.5KW Fan Extractor (In the Booth)

2.5KW Heater (In the Booth)

6x 70W Fluorescent Fittings

1x 500W Halogen Security light, used as a second light in the Booth.

4x Sockets

Maths:

Max Demand (Ib) at the Outbuilding using diversity on the lighting only = 50.56A

I've used a 20A Radial for the sockets, so 30.56A from everything else + 20A

In = 63A (even though it's just over 50A)

It = 63A (External run, but no Ambient Factor applied)

VD = 13V (Over 5%, or should I use 3% as I have lighting in the outbuilding?)

Cable Selection SWA Clipped Direct along a Concrete Fence Support. Now based on 5% both 10 & 16mm too small for VD.

Any way of reducing the Max Demand at the Outbuilding? I know the Fan & Compressor will be on together along with the lights. I'm assuming the heater is used afterwards almost as a baking process & sockets, well maybe he'll now plug in a radio or phone charger, or small hand tool - Grinder/Drill?

Also, it got pointed out that I might need to be aware of the conditions of switchgear & ventilation due to the spray booth. He has a Main CU & Sockets etc already in there (outside of the booth) & uses a Gas brazing torch in the same environment, so if explosive/flammable environment due to paint he's using, I'd have thought there'd already be an issue?

Any pointers? I did work out R1+R2/ZS/Fault etc but then realised I was over on the VD...

 

[batty]

There is really to much design criteria here to discuss on an open forum. I would actually need to see a job before giving answers. If you only work as a mate how will you sign this job off surely you are not registered for part p. My only advice would be put in a bigger supply than what you think is needed and I probably would be concerned with the 60a main fuse. What power is being used in house although I would think the power would not be needed all the time in the workshop so a 63 amp supply is probably overkill anyway? Some of the more commercial guys will probably no more on what is needed for the spray equipment.

 

[steptoe]

its the spray equipment that gets me,

I would think its NOT water based paint, so therefore becomes an EX zone, I dont know enough about this stuff, and Im not insured or qualified to do work there,

so, Im out.

 

[claret73]

I'm almost thinking I'm out too!...I think it's cellulose but not asked about that yet. With regards to the post about certification, the Contractor who has trained me past 3 years would be willing to certify as I've talked a little through with him but not in detail as I've not seen him...

 

[pickleye]

Sorry, had a long week, so may of miss read. But, if this is not over loading and popping a 13 amp plug top fuse, is a 63 amp supply needed?

Taking out the rcd is fault not overloading, or am I missing something.

I'm not saying 60m 2.5mm and the present setup is good, but from 13 amp to 63 amp supply without any change in use "just tidying up" current supply. Maybe checking diversity again worthwhile, before customer/mate looks at estimate

 

[claret73]

I'm sure he said it's tripping the breaker not the RCD. I didn't look exactly at what the armoured in the house was wired into. It was into some kind of plug in adaptor, yet non of the armour was into it. Taking the load of equipment in the outbuilding, I'd need to reduce it by diversity but don't see how as everything but the lights are power circuits. Designing this is proving a headache. Not a standard cable calc & then there's the issue of the ventilation...

 

[mikep]

Have I got it right or am I confused yet again!!!

2.5mm running 60metres from a plug thing in the house, then compressors, heaters, sockets, extractor, more heaters& light's.

Can't figure out the nuisance tripping with that lot.

 

[claret73]

Can't figure out the nuisance tripping with that lot.

I can, just not with the redesign...unless I'm getting confused? Which of course I am...

 

[pickleye]

2.5mm SWA wired into some kind of plug in adaptor to a Socket Outlet.

Causing nuisance tripping I believe or could be taking out the RCD on the Board in the House.

I interpreted that the current system is not getting added to or being used more just re-supplied.

So if it's running off a socket outlet at the minute with no sign of heat damage, not blowing fuses or breakers, but nuisance tripping the rcd assessing the load at over 50 Amps is probably worth reassessing.

For example, Compressors generally run to fill a reservoir then turn off so not a permanent load. My dad ran a compressor, lights, small power tools and stick welding set off an extension lead for years. Replaced the plug top fuse every now and then when the rod stuck. I'm not saying that was good.

However, 50m of 16mm 2 core swa is 208 quid plus vat from tlc. how serious is client about getting job done?

I know nothing about the considerations for the paint fumes.

Again, i'm only an apprentice so take note from pros.

Hope this helps

 

[unphased]

Hi Claret. If you design for a 40A supply, notwithstanding your maximum demand calcs which are kinda estimates anyway, then I would have thought a 40A supply (9.2kW) would be enough for the equipment mentioned. That should get your VD down and a 16mm2 2-core SWA is adequate. This looks right to me.

 

[NozSpark]

its the spray equipment that gets me,I would think its NOT water based paint, so therefore becomes an EX zone, I dont know enough about this stuff, and Im not insured or qualified to do work there,

so, Im out.

Same here,, I wouldn't touch it

 

[SLIPSHOD & SLAPDASH]

I reckon you have seriously over estimated the demand. A compressor may surge on start up very high, but probably runs on about 5A. I also doubt the extract fan runs on 1.5 Kw