Fused Neutral

the pict · Jan 4, 2014

I have had a preliminary look at a job I am quoting for,it is a 3 phases are protected by 100A fuses as is the neutral, am I right in saying that the practice of fusing neutrals is a departure or is that just in final circuit distribution, I will be refering to the regs later today on some other matters but if anyone can give me the heads up on this particular issue I would be gratefull
Pict

RyanCheetham · Jan 4, 2014

The neutral may have a blank inside the carrier rather than a fuse

telectrix · Jan 4, 2014

a lnk would be a better description. a blank implies there's nothing behind the cover.

the pict · Jan 4, 2014

I am aware that the regs state that a fuse should be fitted in the line conductor only but I cant ascertain if this reg refers to the incoming supply, as to the possiblity of a unfused link inthe N I cannot say but it definately says 100A on the holder
P

telectrix · Jan 4, 2014

it says persil washes whiter on buses, but they don't take in washing. you can't go by what label is on the holder. the " no fuse in neutral" applies to supply fuses as well as for final circuits.

the pict · Jan 4, 2014

Cheers Tel 132.14.1 & 14.2 are vague and do not specifically mention incoming supply , so thanks for adding clarity
Pict

telectrix · Jan 4, 2014

i would say that that is because BS76571 does not cover DNO's equipment.

the pict · Jan 4, 2014

your right of course, and once again another round of phone calls to get them out with the usuall " can I have the customer account number,the post code, can the engineer park at the premises, will he need a ladder, will the customer be present, are there any dogs at large, etc etc thats if I get through to engineering at all as they have changed all the numbers I had
Pict

Engineer54 · Jan 4, 2014

The only time you will see a fused DNO neutral is on very old service heads that will almost certainly be of cast iron construction. If this is what you have then contact your DNO to replace.

These old service heads have been deemed dangerous and should have all been replaced by Sept 2011, but there are still thousands of the things still left in service.....

polo1 · Jan 4, 2014

As Eng has said, there are 1000's of these old cut outs around - I've had four replaced in the last few months. To be fair, Scottish Power change these on request foc (though I always say they are crackling, warm etc!).
On Arran, I'm guessing it's SSE?
Managing to dodge the worst of the storms Pict? I saw Ardrossan yesterday - very breezy!

Lucien Nunes · Jan 4, 2014

On a 3-phase 4-wire service it was never correct to fuse the neutral and I have never seen it done. This is due to the likelihood of over-voltage on the load side if the neutral is interrupted, i.e if any unlinked protective device opened it would create a dangerous situation. No matter what kind of service head you have, it should contain a link rather than a fuse.

On single-phase service, until 1943 it was considered beneficial to fuse the neutral because it was not assumed that neutral was reliably earthed, so there could be fault conditions that a fuse in the line (live, as of 1943) would not protect against. But a change in the ESR1937 made it mandatory to keep the neutral solidly earthed, so the revision to the 11th edition recommended single-pole fusing instead.

the pict · Jan 4, 2014

Hi Polo Yesterday saw a really high tide but not as bad as the mainland but the south of the island caught the worst of the high tide and storm surge, me I stayed put with me beer
Pict

Knobhead · Jan 5, 2014

I came across many early service heads with fused neutrals. Originally the supply was DC two wire. The service heads had a glass panel for the rewireable fuse bridges.

Engineer54 · Jan 6, 2014

On a 3-phase 4-wire service it was never correct to fuse the neutral and I have never seen it done.

Very true, nor have i, though i dare say it has occurred in the past. My fault for not reading the OP properly, totally missed the stated 3 phase bit!! lol!!

gnuuser · Jan 6, 2014

ive seen a few fuse blocks (tip out type)similar to these

with steel links labelled neutral only (fusing a neutral here is against code as well)
and had to explain to the apprentices and production twits why the cant put fuses in them

Fused Neutral

the pict

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RyanCheetham

telectrix

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the pict

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telectrix

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the pict

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telectrix

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the pict

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Engineer54

polo1

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Lucien Nunes

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the pict

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Knobhead

Engineer54

gnuuser

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