workshop electrics

[KrashBandiKoot]

Hi folks, I found this forum when I was looking for a bit of help with a 2 MCB fused consumer unit I'm going to install in my workshop.

OK just to outline what I'm doing, (in order to get the best advice I can), I'd like to double protect my tools and workshop by having a single cable from the house consumer unit powering the workshop consumer unit which in turn will have a fuse for the lights and a fuse for the sockets.

Now, having done a bit of research on this, I find because I'm going to be running florescent strip lights, (a total of 4 of them each offering 58 watts of light), and several transformer based 12v halogen lights as well as 3 energy saver light bulbs drawing about 18 watts each.

So given this, would I be right in assuming a 10 amp fuse on the workshop consumer unit will be more than enough? I have read a 6 amp should be fine but because I'm running halogen lights with transformers, (a total of 4 of them all wired to its own light switch), they tend to trip out 6 amp MCB's.

Would I also be right in running a 16 amp consumer fuse for the sockets circuit?

I'm going to install a total of 8 double faced sockets with each socket unit running a 4 strip surge protected socket.

Now, the biggest consumer units I'll be using are a 150 amp Arc welder, a 100 Amp MIG, a 768 watt or 3.2 amp compressor and a 1,100 watt table saw though not at the same time of course

The maximum draw on this will be:

All the lights, (4 halogen 100 watt transformers), plus the 4 strip lights, a stereo amplifier and perhaps the table saw and the compressor at the same time though the air tank on the compressor will be fully charged and it'll only flick on to top the tank up from 50psi back to 110 psi.

Given this, would I be better using a 25 amp MCB on the house cosumer unit or a 32 amp?

Everything in the workshop runs off a 13 amp fused plug so nothing is wired into the system directly.

I would also ask, would be better off putting a radial circuit or a ring circuit for the sockets?

Of course when it comes to wiring into the houses main consumer unit I will be calling in a qualified and registered electrician rather than doing it myself.

I'll add, so far I've been running the lights and sockets off a single 13 amp fused plug with no issues at all but I'd like to change that to a more permanent and professional solution that will offer me and my tools better protection from surges or the risk of electric shock.

Also, would I be OK to run a single light off the plug sockets? It's just that of something did go wrong with the lighting circuit, I feel it's not a good idea to be plunged into darkness while running material through the table saw since I like my fingers where they are

Thanks for the help

 

[PrenticeBoyofDerry]

First thing you need to access is the load within the garage and the likelihood of what equipment will be depending a load.
Welders tend to have an inrush current that raises above the working current on start up.
A 6 Amp lighting circuit can handle 1350W load.
Your socket outlets will require RCD protection as will any buried cable.
I would personally take a circuit from the house CU that was not protected by an RCD. Then depending on the length of cable between house and garage that would determine voltage drop and size required.
This circuit I would protect by 40A MCB on SWA cable.
Then at the garage unit I would have a radial socket circuit protected by 32A RCBO on 4.00mm cable, and the lights on either a 6A MCB if cable is surface mounted or 6A RCBO if buried within the fabric of the wall, 1.00mm cable will be satisfactory.
It is always wise when using power tools to have a second source of lighting.
As this work does require new circuits, it is deemed notifiable work.

There would also be consideration to be made with regards to main earth bonding and earthing arrangements.

 

[ericmark]

Starting in the middle so to speak what size cable feeds to garage consumer unit? Size of MCB in the house will match the lowest current carrying capacity of the cable between garage and house.

So if for example your using 6mm² twin and earth between house consumer into and a adaptable box even if 10mm² SWA after that it will be limited by the 6mm² so around 32A.

If cable not already there then it's a case of doing sums likely you will need a 32A socket for welder as unlikely under 16A and there is nothing between the two sizes.

Distance and earthing methods will also be a consideration what earthing method does the house have?

In the main lights will have something which limits the supply to 6A although the regs allow up to 16A normally there is something like a ceiling rose limiting to 6A and even if there is not when bulbs blow if over 6A often they will weld into the holder. Florescent is normally OK as 3A fuses inside the fitting but switches are normally 6A so likely two feeds required.

I would consider a 10mm² feed and a 45A in house with 6, 16 and 20 amp MCB's in the consumer unit feeding lights, 13A sockets, 32A sockets.

But you will need to calculate it all as clearly new circuits so will need to inform LABC who will likely inspect and test so praying the ELI is within limits is not really good enough last thing you want is to rip out and start again.

 

[EFLImpudence]

If you want the electrician who you say is going to connect to the house to certify this legally notifiable work then he will have to supervise the work you do.

Therefore it would be advisable to employ him and discuss everything you require as it is not really a DIY job without being spoon-fed on every step.
Then he can tell you what to do.

There are many safety factors which you don't know you don't know and necessary testing equipment which you don't have.

 

[KrashBandiKoot]

Just to clarify, it's not a garage, this is a custom made workshop built from the ground up out of wood so I can avoid the obvious planning permission as it won't be a permanent structure/

As far as tools go, to list the main units :

Table saw
Routers
Ben joiners
Drill press
Miter saw x 2
60 Amp boost charger for batteries
Arc welder, (150 amp)
Mig welder (100amp)

Then on top of all of that it's the usual run of the mills tools such as cordless power driver battery packs, (at least 4 of them), drills, sanders, planers, etc.

It's basically a place to park my bike and use as a wood work shop for custom built furniture.

With respect to the cables, from the house consumer unit I'm using a heavy duty dedicated outside cable which I believe is 4mm

With regards to the sockets I'll be using 2.5mm cabling and for the lights standard 1mm.

The house itself has a standard earth which is basically a spike in the ground as well as earth clamps on the metal piping for the water and central heating system. I'm intending to add another earth at the workshop consumer unit which will be a spike and an earth clamp in addition to wiring the unit itself to the houses earth wire.

As I said, I'm intending to operate a 2nd light system above the table saw with will be plugged directly into the sockets so if the lights trip out I'm not without any light at all. It doesn't matter if that light goes out due to a socket trip as any tool I'm using will also power down and in my experience, when table saws trip when cutting stock, the blade tends to stop rather rapidly due to the motor brake and the friction of the stock being passed through the blade.

I do think though that putting in a 40 amp MCB fuse on the house consumer unit seems excessive so would question this?? Wouldn't it be better to have a lower rated fuse in there, (a 32 amp), so if the draw exceeds the supply ability then it's more likely to trip the workshop consumer unit first rather than trip both at the same time?

What I need to be careful of here is the potential for a blow out and sparks, especially in a place where there will be a lot of dry timber and lots of saw dust as well as other combustible materials such as thinners, stains and varnishes not to mention 25 liters of petrol in the bikes fuel tank.

 

[KrashBandiKoot]

If you want the electrician who you say is going to connect to the house to certify this legally notifiable work then he will have to supervise the work you do.

Therefore it would be advisable to employ him and discuss everything you require as it is not really a DIY job without being spoon-fed on every step.
Then he can tell you what to do.

There are many safety factors which you don't know you don't know and necessary testing equipment which you don't have.

Actually, 20 odd years ago I was installing fire alarm systems on inshore oil rigs and rewiring domestic houses so I'm good on the actual installation. I don't mind leaving socket and switch faces off for the electrician to check the work/connections before certifying it.

The issue is my practice is some 20+ years old now and I'm not JIB registered so can't re-seal the main fuse with the required wire and sticker seals simply because I don't have access to such things so need someone certified to make the final connections and sign the work off which shouldn't be a problem.

 

[EFLImpudence]

No, you need someone to certify all of it - design, construction, inspection and testing.

Either the LABC if they deem you competent or a registered electrician.

 

[ericmark]

It does not matter if workshop is in open air it takes power from the domestic premises so it is notifiable work in England and Wales.

Working on biggest item 150A welder output voltage approx 25v plus 1 volt for every 25A so 31 volt total so no losses 31 x 150 = 4.65kW = 20.22 Amp so 25A is the lowest supply you could possibly use. Likely you will need a C25 MCB for welder so will need a loop impedance of 0.92Ω and a B32 will trip before a C25 so will need a B50 supply for the C25 to trip first.

It's simple maths and if you have the skill to design you will have to do the maths yourself you can't expect others to do it for you.

 

[Taylortwocities]

The house itself has a standard earth which is basically a spike in the ground as well as earth clamps on the metal piping for the water and central heating system. I'm intending to add another earth at the workshop consumer unit which will be a spike and an earth clamp in addition to wiring the unit itself to the houses earth wire.

You say that you ("I") will be doing this. What happened to the electrician?

You will not have another earth spike IN ADDITION to the house one. You have a TT installation. You need an earth spike for the shed alone and separate to the house earth.
Your electrician will have to do this, unless you have an earth impedance tester that will be able to tell you that the impedance of the earth electrtode is adequate.

PS they aren't earth clamps.

 

[KrashBandiKoot]

You say that you ("I") will be doing this. What happened to the electrician?

The electrician is required ONLY for the final connection - From the workshop to the consumer unit in the house because I don't the relevant JIB registration, wire seals or sticker seals to reseal the 60amp main fuse.

If I had the wire and sticker seals I'd carry out the work myself and save myself £95 an hour plus VAT for the 1st hour then £50 an hour plus VAT for each hour after.

I am rather puzzled as to exactly why I'd need a 40 amp fuse since that's usually for a shower unit and typical domestic ring/radial circuit on sockets has only a 16 amp MCB.

 

[EFLImpudence]

The electrician is required ONLY for the final connection - From the workshop to the consumer unit in the house because I don't the relevant JIB registration, wire seals or sticker seals to reseal the 60amp main fuse.

Wrong. My previous post is correct.

If I had the wire and sticker seals I'd carry out the work myself and save myself £95 an hour plus VAT for the 1st hour then £50 an hour plus VAT for each hour after.

OK. Enough said.

I am rather puzzled as to exactly why I'd need a 40 amp fuse since that's usually for a shower unit and typical domestic ring/radial circuit on sockets has only a 16 amp MCB.

Q.E.D.

 

[securespark]

Who mentioned 40A?

And if you have a 60A main fuse, it may need upgrading.

 

[flameport]

I am rather puzzled.

You are not the only one.

No electrician will show up and just connect a load of wiring to the supply - it will need to be tested, and before that, confirmation that it was actually designed and installed properly. Given the posts so far, all of that seems very unlikely.

Why would the main fuse need to be removed when connecting a new circuit to a consumer unit?
What has JIB membership got to do with anything?
Where did £95 an hour come from?
Or 16A ring circuits?
You are concerned about 'blow outs and sparks' causing issues with petrol, sawdust and thinners, yet will be using heavy duty welding equipment in there?
You rewired houses 20 years ago, but have apparently forgotten everything, including the most fundamental aspects?
Structures are exempt from planning permission simply because they are made of wood?

Clearly this thread is a wind up.

 

[KrashBandiKoot]

It does not matter if workshop is in open air it takes power from the domestic premises so it is notifiable work in England and Wales.

Working on biggest item 150A welder output voltage approx 25v plus 1 volt for every 25A so 31 volt total so no losses 31 x 150 = 4.65kW = 20.22 Amp so 25A is the lowest supply you could possibly use. Likely you will need a C25 MCB for welder so will need a loop impedance of 0.92Ω and a B32 will trip before a C25 so will need a B50 supply for the C25 to trip first.

It's simple maths and if you have the skill to design you will have to do the maths yourself you can't expect others to do it for you.

Design? Design what exactly? An electrical system? LMAO!!! Yeah, there's a real lot of "design" going into ensuring there's a series of sockets available near to work benches.

And of course there's a hell of a lot of "design" in ensuring that light is cast where it's needed eh? Don't talk such utter rubbish please, there is no design in this, it's called common sense. Do I need a socket where I'm going to be welding? Yes - Install one!

Do I need good lighting where I'm going to be welding? Yes - Install one!

Do I need a socket/light where I'm going to be sanding, drilling, cutting, routing? Yes - Install one.

There are no plans to this, it's all about where to site the bench tools for there's ample room for long/wide stock and add a light to that area.

The bottom line here is that I could do what I'm currently doing, run the whole workshop off a single 13 amp fused plug that's plugged into a wall socket as this has worked well so far. I've used the arc welder, had the stereo going, the computer, had batteries on charge, all the lights on and even been charging a car battery at the same time without fuses blowing so why there's this need to over complicate and talk of designing escapes me somewhat.

Yes I'll admit I'm not ofey with the current regs or ratings which is why I've asked the questions I've asked.

The bottom line here is a simple question, if I'm using a 16amp main fuse for the sockets and a 10 amp main fuse for the lights do I need to put a 25 or 33 amp fuse in the consumer unit in the house since that one fuse will in effect be running two separate fuses and two separate systems.

Other than that input isn't required thanks all the same, so the maths you've produced seems silly since a single 16 amp main fuse and a single 13 amp plug has run everything very easily so far without any issues. The main aim is to get the workshop, (not shed, it's a professional workshop not something knocked up by an amateur out of bits and pieces but is built from stress graded stock), off the houses socket ring and onto its own supply.

Sorry if this post seems tetchy, that isn't my intent, however applying needless maths and going off on tangents really isn't required. It boils down to one simple question - Does the main consumer unit fuse need to be 25 amp or 32 amp? So if someone could answer that definitively I'd appreciate it, if not then fair enough. I'll ask the electrician I employ and go out and buy one for him to install when I'm ready for the final connection to be made as I'm not paying a 300% mark up and £12 on a fuse that will cost less than £3.

 

[flyingsparks]

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