Earthing a loooooong cable?

Depends on the size of the cable and what ovrcurrent protection you have and wether you are using an RCD. It is extremely unadvisable to go outside the main equipotential zone (essentially the house) without RCD protection

Since you can get anRCD plug top for under a tenner there is little excuse for not doing so.

In article , Douglas de Lacey writes

Why not do the job properly, armoured direct buried cable etc.

You can get all the parts and good advice from Cambridge discount electrical at the bottom end of Mill road in Cambridge!....

Just asking. AIUI the RCD protects the against cable accidents 'downstream' of itself, so it would be plugged into the house circuit. Would it stil work effectively on 50 metres of cable?

I can't see that an RCD would ever loose it's effectiveness with any cable length, as it senses current imbalance irrespective of voltage. Certain sorts of loads on it may cause nuisance tripping however.

Why not? RCD works by, in effect, noticing that some of the current going out is not coming back. Length of circuit doesn't come into it. RCD doesn't protect against a live to neutral short so you still need a fuse.

One other factor to consider is the voltage drop in the cable. 50 meters of 1.5m^2 cable will have a loop resistance of about 1.5ohms. The voltage drop at 10amps would be 15 volts which is probably OK

I would think the answer to that is cost. A permanent outdoor electrical installation is not a DIY job. You need an approved contractor to do the job, part P approval etc.

Much easier to run a tempory cable. Not as safe but then part P never ws about safety.

I would think the answer to that is cost. A permanent outdoor electrical installation is not a DIY job. You need an approved contractor to do the job, part P approval etc.

Much easier to run a tempory cable. Not as safe but then part P never ws about safety.

Think AC and capacitance from e.g. live to earth..

It certainly can be a DIY job, but requires you to submit a Building Notice to the council.

Part P exemption just entitles some people to do the work without submitting a building notice.

Much better to stuff part P where it belongs, and do it the right way!

What sort of live/earth capacitance does T&E cable exhibit per metre?

Wouldn't this manifest as a small impedance (1/jwC)?

As any live/earth capacitance is being charged/discharged at mains frequency how would that affect an RCD?

I'm not aware that the IEE wiring regulations has any limitations on cabel length following and RCD - what in particular is your concern?

Yes, cost and inconvenience of Part P. I am seriously considering John Rumm's advice but there are reasons why I'd like to keep it legal:-) -- and I don't see it's any less safe. Inclusion of an RCD goes without saying, by the way.

Douglas de Lacey

Do you actually intend to leave this extension lead permanently in place or just run it out when you need it and coil it up when you have done?

About 10 metres of 1.5mm is the max for PAT (test).

Should do: the current required to trip an RCD is orders of magnitude less than required to trip an MCB and easily within what you'd get on

Haven't decided. At some point it will cross the lawn so will need [re]moving whenever the lawn is mown. Idleness will no doubt dictate longish spells in situ. Was there a reason for the question?

Douglas de Lacey

Hum. Am I supposed to PAT test it?:-) What's the minimum size for 50m? (And, JOOI, what's likely to be the diameter of the average 25m extension cable?)

Douglas de Lacey

Can you explain your recommendation?

Yes, PAT testing of power tools is a good idea. Though very few diy'ers do it I imagine.

Shouldn't the extension lead should be tested seperately from any device plugged into it?

Isn't the limit about the impedance on an earth continuity test (ideally high current), something like 1 Ohm rather than a specific length?

But when Prescott is found frazzled with a bit of old colour twin and earth stuck up his arse just how many uk.d-i-y suspects will there be?