Grandmothers fuse-box

[Graham]

My late maternal Grandmother lived in a largish semi-detached house in North Manchester until the early '80s Her CU was interesting. I think it was intended for industrial use. It was metal, IIRC it was made by MEM but here's the interesting bit, it was double-pole. Let me clarify, each circuit was wired to a pair of fuses, one off the live busbar and one off the neutral.

When I became wise enough in these matters to realise the dangers, I rewired the neutral links with heavy wire and labelled them as not to be removed. Why have fuses in the neutrals?

One thought I had is that it was made for a dc supply. Did they fuse both poles in that case?

Oh yes, and she had Wylex sockets with the in-line-pin plugs.

[John Rumm]

It may have been intended for use with a generator that had a "floating" output (i.e. neither side strapped to earth - or even a centre tapped output with the centre strapped to earth). Hence either side could appear live wrt to a local earth, and possibly pass substantial fault current if connected to earth)

Long time ago, when neither side was earthed anywhere in the distribution system...

[Dave Plowman (News)]

My parents house was built like this in the '30s. I think, as you say, a hang over from the DC days. But it was always AC.

[Owain]

Quite normal until the War, with both AC and DC supplies, because neither side of the supply was reliably tied to earth.

Still the case in some European countries although they have DP MCBs now.

Owain

[<me9]

It was the case well after the war. My parents had additional sockets installed from a new double pole switch fuse (both switch and fuses) using TIR cable in the late 50s. This must have been in use until the house was re-wired (the lights and other original wiring was lead covered dating from the 30s) around 1964.

I rewired my sister's house in the early 70s after the (DP)lighting fuses (in a wooden fuse box) kept blowing. The wiring was single insulated single core rubber covered, and was under wooden capping.

I'm sure both complied with the relevant IEE regulations at the time they were installed.

As an old colleague of mine stated, as long as it was installed under wiring regulations (any edition). At least some form of risk assessment had been made, but both ended up beyond the sell by date.

Periodic inspection was more relevent then than now.

[meow2222]

If you read the wiring regs, such as they were, from the 20s/30s they make scary reading. Phrases along the lines of we recommend not having bare live bits, but its ok to ignore this.

NT

[Owain]

Well, if people are stoopid enough to touch the shiny brass bits ;-)

Owain

[<me9]

It was reputed (at a place I worked at 35 years ago) that a routine check on the switchboard (a 3 phase 415 volt supply with open knife switches for isolation, with a normal load of several hundred kilowatts) had been to feel the (live) poles of the knife switches (one at a time whilst standing on a

3/4 inch rubber mat) for signs of excessive heating.

Someone decided to speed up the job by checking two switches at a time (415 volts between phases). The routine was promptly dropped. I'm not sure of what happened to the person checking.

[Owain]

Excessive heating, probably.

Owain

[John Kenyon]

Too much smoking and not enough breathing probably...