Looks like I'm going ahead with 3 phase into the new workshop. This is mainly to power fixed machinery, but some socket (welders, compressors etc.) would be useful too.
What's a good book to start reading? My current 16th ed on-site covers almost nothing useful here. Is there an industrial equivalent?
There's also the issue of the workshop being near to, but separate from, the house itself. Some "workshop" "sheds" are inbetween them (connected to the house, if anything). One of them is a place I'd particularly like to have robust sockets (physically and electrically) to drive welders. What are the issues about supplying this either from the house or the workshop incomers?
Andy Dingley coughed up some electrons that declared:
Commando sockets (16A or 32A) any good?
You'd normally (in my computer room experience of those) run them as radials, often with only one socket per circuit if it *is* going to be used all the time.
Do you want 3 phase or single on those (either is available)?
The only issue I've come across with outbuildings is whether to export the house earth to them or to have a local TT rod + suitable RCD protection.
There was an IEE Wiring Matters article on this IIRC - want me to dig out a URL?
Adam (to cite just one) will know a lot more about this, so I'm not volunteering much 'cos I've not touched a lot of 3 phase.
Anything that deals with the full regs. Your local library ought to have something.
Three phase is run as radial circuits. If for an industrial installation and subject to HSE inspection, each machine must be provided with local isolation and an emergency stop.
Good practice, although not mandated, is for single phase socket outlets or lamp sockets on different phases to be at least six feet apart. Personally, I also colour code socket outlets with a bit of tape around the conduit leading into the box, so you know when you might be bringing two phases into close proximity.
Any place where single phase might be expected, but where two or more phases are present, for example inside a multiple light switch, must be marked externally with a warning of the higher voltage.
Make sure it is from one or the other, but not both, to avoid the possibility of having some circuits live when you think the supply has been isolated. As already mentioned, you also need to decide whether you are going to export the earth or have a local earth.
I'm used to factories where the lighting load needs to be balanced across phases, let alone the single phase socket outlets. However, for a small workshop, where there is not likely to be a need to balance loads, that would be a perfectly acceptable answer.
On Mon, 20 Oct 2008 18:56:00 +0100 someone who may be Tim S wrote this:-
The 32A size and above should always be wired on individual circuits.
16A sockets may be wired more than one to a circuit, if diversity allows for it to be done. That is useful for sockets which are seldom likely to be used simultaneously.
Yes - I can see that. But in a large building it would be fairly easy to group stuff to minimise the risk of having adjacent outlets on different phases?
I was thinking of TV studios where they tend to keep all GP outlets on one phase but where the large load, ie lighting, is on three. The thinking being that you're more likely to get some form of fault on a portable appliance fed via an extension lead than something which is near permanently plugged in.
The request for service is quite adamant about the need to balance anything and everything. Although as you rightly say, the actual load here is going to be trivial, they don't have a tick box for that. 8-(
I'm likely to plan for four load groups: 3 phase machinery, hard-wired single-phase machinery on one phase, sockets on another and lighting on the third. I certainly don't fancy mixing the sockets across phases, nor do I see any real need to. Lighting load isn't big enough to require it. The biggest realistic issue would be splitting the few simultaneous loads like the compressor (hard-wired) and a plasma cutter (socketed single-phase) onto separate phases. Worst case otherwise is single-phase dust collector and single-phase sawbench both being on the same phase (hard-wired singles) and likely to be used together, but they're both only
Is there a formal definition of "it" in the regs? The main workshop and garage is free-standing and has the 3 phase entry through the rear of it. There's another workshop which is "attached" to the house (via a row of outbuildings) and that's where I'm likely to want to weld. Now for the effort of running SWA under the concrete path, I'm happy to power this entirely from the workshop 3 phase and can easily have physical separation of a wall, exterior door or 6' spacing between that and any house-fed outlets. However this would mean I'm running two supplies into one connected "building" and I was wondering if that was the point that "nearby" would be regarded as starting to apply.
Not sure on that either. I'm not thinking about local earths so much as the two separate ones supplied by the 'leccy board, entering from different directions (and quite likely, different substations). Do these need to be deliberately bonded, deliberately isolated or what?
Andy Dingley coughed up some electrons that declared:
The first thing to do is to gather some of the pertinent parameters:
If any earth were to be exported to a particular building, it would usually be the one from the associated supply to that building, but see below...
If I understand you correctly, the 3 phase supply head and meter are in the garage/main workshop and the house has it's own supply. I guess the main workshop would best rely on the 3 phase supply's earth - but wait for some more opinion. It's certainly the more straightforward case.
And you plan to continue this 3 phase supply onto the workshop hanging on the side of the house?
Do either of the workshops have a lot of exposed metalwork that may carry an earth potential (framing for example)? How far apart, roughly, are the two workshops?
What type of earth are on your two supplies: TN-S or TN-C-S? Or are either TT (other than TT, this needs to be done by enquiry, looking at the supply head isn't a reliable method, unless it's actually labelled - my supply is TN-S but looks exactly like a TN-C-S takeoff).
*** This is important *** Is there any metalwork (pipes etc) that goes between the house and the workshop connected to the house? This is were it gets hairy, because the metalwork will be introducing the house earth potential to the workshop and vice-versa.
If so, I bow out - I have no idea how to handle this, other than to TT everything, house included and add 100mA time delayed RCDs as required. I wouldn't go bonding two different supply earths together (especially if they may come from different substations) without getting more informed opinion and it's way beyond me.
I think most of the questions I've raised are relevant, so the answers may help someone more informed to offer advice.
In one factory I had, the vast majority of single phase sockets served a row of individual work benches along one wall. As the benches were 1.8m long, it was necessary to have a couple without sockets - fortunately not difficult, as they carried hard-wired machinery used by all the instrument makers..
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