OT:- Trippin mains - Electricity gurus in da house?

Sorry about the multiple posts, Google is in a bit of a state at the moment!. Greg

If you're talking about a domestic installation that's a popular myth, the person doing the work has to complete the Electrical Installation Certificate and to do that they have to be a competent person in the eyes of the law. This then has to be submitted to the building regs department who won't accept one from a DIYer, they will insist on sending one of their inspectors both before, after and in some cases during the work work and charge you dearly for the privilege. They won't accept being presented with a finished installation that's all covered up and impossbile to inspect properly.

Normally an inspector can not fill in an Electrical Installation Certificate for someone elses work, all he can do is a Periodic Inspection Certificate (often called a landlord's certificate) which is a far less vigorous inspection as it does not check things like hidden parts of the installation. But new work legally requires the former, so you can't just get someone to inspect your work.

There are some exceptions:

Some very small items like replacing a light switch are non-notifiable under part P, a Google will tell you what you can legally do yourself, but you still have to be competent and fill in a Minor Works Certificate, but what DIYer has the test kit to do that?.

A sparky who is a member of a competent persons scheme such as NICEIC does not have to submit the certificate to building regs, though he strill has to fill one in, he just notifies NICEIC on-line who do it on his behalf and guarantee his competence to self certify.

A company who is registered with NICEIC etc can have nominated inspectors who can fill in the certificates for their employees who don't have to have the same qualifications, though insurance companies are effectively compelling such employees to have at least C&G 2381 (the wiring regs) it does save them all having to have the much more demanding C&G 2391 (Inspection and testing).

The bottom line of course is that no one is checking up on people, and any one can buy materials and equipment at B&Q that they aren't competent to fit. Of course if your house burns down and the insurance company refuses to pay a penny because it was caused by illegal work you may regret it... Greg

Me (a most positively DIY electrician, albeit with a fair bit of experience in the electrical industry). An insulation tester, a RCD tester, an earth loop impedance tester and quite a lot of other toys as well.

Large as in physical or large as in power rating? From what you say it sounds as if the starting system doesn't stage the start to limit starting surges. Motor windings are basically a dead short at switch one but that shoudn't upset and RCD only an overload device. What will upset the RCD is an overly large start/run capacitor. As that initially charges up current is flowing into the device but not coming back, the RCD assumes that this current is going somewhere it shouldn't and disconnects.

I to am surprised you can hold the RCD in. Could you change it for a time delayed type? They are normally used over here for whole installation protection when the earth loop impedance is too high but are 100mA leakage. You need 30mA for shock protection, not sure if you can get time delayed 30mA ones though.

Agreed, a very sensible approach. Especially for kit that is bumped and transported about.

And as the majority of electricity used ends up as heat what do you do with 13 x 6 x 230 = 18kW of heat in a room. B-)

Individual rings are also limited to the floor area they can serve as well, 100 sq meters I think.

Or wander off the any of the makers sites and get them there.

Fair enough, but I don't think you're typical of the average DIYer 8-) Greg

On or around Wed, 13 Dec 2006 08:19:41 +1000, Duracell Bunny enlightened us thusly:

does the RCD have an overload aspect, and is it this that's tripping it?

If I try to start my lathe from cold in too high a gear, the starting current in the motor trips the overload before the machine's up to speed. This has got better since I fitted a larger capacity starter switch.

RCD should be comparing line and neutral current (on a single phase thing, anyway) and I'm not really sure how startup surge would cause an imbalance in currents in this way.

In the case of my lathe, the motor is 1.5HP so about 1.1Kw, and once running only draws about 5A. The starter that was on it when I got it was adjustable up to about 8A overload trip, and regularly cut during startup if the oil was cold. The replacement starter does 9-14A and is set at about

On or around 13 Dec 2006 01:10:25 -0800, "Greg" enlightened us thusly:

OK, we heard you the first time... :-)

I've got a new consumer unit awaiting wiring in with MCBs instead of the wired fuses we have now. No doubt this will allow heavy loads in the workshop to cut off all the power to the yard... although I think I specced a 40A MCB for that line...

The 40A feed to the workshop could be changed to a type C or even D if you have nuisance tripping, but you need a much lower earth fault loop impedance for these, I have a C on my garage feed. Greg

And as this is an exported feed (ie it's outside the building that has the supply) you need to pay particular attention to the earthing.

Exporting earths is not particulary good practice. Probably best to bung a good local earth spike in at the workshop end of the feed and protect the whole installation with a time delayed 100mA RCD. I suspect you could split the feed in the workshop, one for "the yard" and one for "the workshop" both sharing the same local earth spike and both have TD 100mA RCDs. This prevents the workshop plunging the yard into darkness or whatever.

There's an echo in here somwhere - echo echo echo

AWEM

This is a farm installation too, so more than 1 spike is probably a better idea than just one.

Steve

On or around 13 Dec 2006 02:01:34 -0800, "Greg" enlightened us thusly:

likesay, I have a megger (as well as the regular mutlimeters and so forth. However, I rather doubt that it's acceptable for actual use these days, being a 250V DC one. AFAIK it still works, though.

On or around Wed, 13 Dec 2006 13:25:31 +0000, steve enlightened us thusly:

I could bond the earth to the steel frame of the barn... that goes into the ground...

You should download the part P regs and have a read of them. I took it that (excluding kitchens and showers and outdoors) if there was some existing wiring you are allowed to add to it and replace as necessary, which gives you a fair bit of grace! :)

I also spoke to a sparky who we employ and he said that all they certify when working residentially is showers, kitchens and outdoor stuff, not anything else.

Seem to recall from my days at college studying electronic principles it has something to do with "skin effect" which means most of the current flows at the outer edges of the cross-section and not much in the middle, so breaking a large csa conductor down into several smaller ones increase the surface area and hence the current carrying capability.

Hope this confuses things even more!

Andy Fox

On or around Thu, 14 Dec 2006 19:52:45 +0000, Tom Woods enlightened us thusly:

Hmmm, p'raps I ort. double-hmmm, wonder if they're in the thing I've already got...

Not very much effect at 50 Hz - is significant at higher frequencies. By 3Khz skin depth is about 1.2mm

AWEM

Formulae here;