Discrimination & Meter Tails

28 Aug 2007
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United Kingdom
I need to have the meter moved further away from the CU to the tails will end up more than the 3m allowed.

Discussions here indicate I'll need an isolator and some means of protection for the new tails and it should be installed in the meter box.

The cutout is a standard 60A fuse. The load is storage heaters needing a 60A supply.

The problem is that I can't use a lower rating fuse to provide both protection for the tails AND discrimination with the cutout.

How can I maintain a 60A load rating in the CU AND protect the tails AND discriminate with the cutout fuse?

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You need to contact your DNO ask for an upgrade to 100A cutout and if they'll agree to longer tails.
You can also see if they'll put an isolator in for you. It may be that you'll have to speak nicely to the guys when they come to fit the new cutout.
Thanks for the quick response!

My guess is that the incoming cable is not up to 100A so this could get very expensive (trench - new cable to joint in field - new jointing box)

I'll give them a call and see what they say.

Maybe they'll let me use 25mm2 SWA between the meter and CU without a protecting fuse...
WeatherMan said:
Maybe they'll let me use 25mm2 SWA between the meter and CU without a protecting fuse...

You won't need a protecting fuse, that's what the cutout is for. Just an isolator. See below.
If your system is PME (TNCS) it should look like one of these
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The way I understand it, is that the DNO are going to be more bothered that their fuse isn't protecting a cable of unknown size and length (rather than calculate things for every house, if they just make sure that 3m of 16/25mm² tails will be alright, then they are covered - thats why they have these limits) than whether or not it properly discriminates or not... to be honest anything causing the submain fuse to operate is going to be a blue moon event anyway, does it not matter if it takes out the company fuse as well? Afterall that is what would happen if the tails were 2.75m and there was no submain

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