Imperial gland - thread size?

[happysteve]

I need to replace this mess with a switch fuse (not the socket, obvs). The pyro is imperial; IR is low(ish) but above the minimum. Estimated age is about 60 years. The only things I'm missing are a banjo and a locking nut. I'm pretty sure I can get a 25mm banjo on to fit, but what thread were old imperial glands? Is it BSP, or something else? This is 1 inch. Where would I get one?

I couldn't see the code on the pot (probably round the back) but it looks like the size that's just shy of 10mm^2 equivalent.

Cheers!

 

[snowhead]

As it's imperial it will be 1 inch conduit thread.

25mm Pirana nut maybe, as 1"and 25mm were very close, we used to thread 1" with 25mm and the reverse, conduit dies, so the nut should fit with maybe just a touch with a file on the threads.

Piranha 25mm Earth Locking Nut | Pratley (BELN25-PK10)

 

[pc1966]

What is the MK box, is it an RCD?

 

[freddo]

Yes an MK rcd.

 

[telectrix]

buy a 25mm to 1" adapter:

1 x 25mm Male - 1" Female Steel Conduit Adaptor METPRO FA3G | Electrical Ironmongery

1 x 25mm Male - 1" Female Steel Conduit Adaptor | This item is manufactured by METPRO | Product No: FA3G | Distributed by Electrical Ironmongery

www.electricalironmongery.co.uk

 

[happysteve]

As it's imperial it will be 1 inch conduit thread.

25mm Pirana nut maybe, as 1"and 25mm were very close, we used to thread 1" with 25mm and the reverse, conduit dies, so the nut should fit with maybe just a touch with a file on the threads.

Piranha 25mm Earth Locking Nut | Pratley (BELN25-PK10)

Ooh, I hadn't considered a 25mm piranha nut, I could ream it out a bit I guess. Thanks!

I only had a 25mm coupler with me in the van to try, and the thread didn't get on very far at all. But a thin 25mm locknut might work, actually.

The question was more about what 1" conduit thread actually was... like: TLC still sell 1.5" and 2" conduit fittings, so I don't need to know what thread it is, I just say what I want. Same with 20mm and 25mm fittings (they're M20 and M25, but I don't need to know that, I just ask for a 20mm locknut or whatever). But no-one sells 1" gland/conduit fittings any more, so if I'm to buy a 1" nut to fit that gland, I need to know whether it's BSP, BSF, NPT (ok, so it's not NPT!), BA, or whatever. For example, would this fit?

Brass Flanged Backnut

BSP thread.

www.toolstation.com

What is the MK box, is it an RCD?

Yes, it's a 100mA RCD. The client installed it - an ebay special - himself a while ago, when he realised there was no protection at all on the submain (apart from the 80A service fuse). At the other end are a pair of lovely metal Wylex 4-way BS3036 fuse boards, feeding the other end of the (very long, and very old) cottage. These will be replaced by a new consumer unit (all circuits protected by 30mA RCDs) and at the same time I'll replace this, err, "arrangement" with a switch-fuse, and terminate the pyro properly - hopefully directly into the switch fuse itself, but if not then a metal adaptable box.

buy a 25mm to 1" adapter:

1 x 25mm Male - 1" Female Steel Conduit Adaptor METPRO FA3G | Electrical Ironmongery

1 x 25mm Male - 1" Female Steel Conduit Adaptor | This item is manufactured by METPRO | Product No: FA3G | Distributed by Electrical Ironmongery

www.electricalironmongery.co.uk

Thanks I might get a couple if these, in case reaming out a piranha nut, or plumbing fittings, don't work

So I've got a few options... still interested in what standard the old imperial conduit threads are, though, if anyone knows. Thanks folks

 

[Lucien Nunes]

I think they are unique sizes not used for anything other than conduit. If memory serves, they were designed by the Simplex Conduit Co. around 1900 and later adopted as a BS. At the time, gas pipe was being used so there were electrical fittings with BSP threads, but the heavy wall was not required and Simplex started over with new dimensions.

 

[snowhead]

The question was more about what 1" conduit thread actually was... like: TLC still sell 1.5" and 2" conduit fittings, so I don't need to know what thread it is, I just say what I want. Same with 20mm and 25mm fittings (they're M20 and M25, but I don't need to know that, I just ask for a 20mm locknut or whatever). But no-one sells 1" gland/conduit fittings any more, so if I'm to buy a 1" nut to fit that gland, I need to know whether it's BSP, BSF, NPT (ok, so it's not NPT!), BA, or whatever. For example, would this fit?

Brass Flanged Backnut

BSP thread.

www.toolstation.com

No it won't fit.
It's 1" conduit thread, not BSP, BSF, NPT, UNC, UNF, BA or anything else.
It's a specific thread for conduit.
The thread is the same angle as Whitworth, but is shallower due to conduit being so thin.

Nothing else fits but conduit fittings.
I've still got my 3/4" and 1" dies, but never had 3/4" or 1" taps otherwise I could have cut a locknut for you.

Not to yourself for the future, if you ever come across imperial conduit save some of the fittings for future use.

 

[happysteve]

I think they are unique sizes not used for anything other than conduit. If memory serves, they were designed by the Simplex Conduit Co. around 1900 and later adopted as a BS. At the time, gas pipe was being used so there were electrical fittings with BSP threads, but the heavy wall was not required and Simplex started over with new dimensions.

No it won't fit.
It's 1" conduit thread, not BSP, BSF, NPT, UNC, UNF, BA or anything else.
It's a specific thread for conduit.
The thread is the same angle as Whitworth, but is shallower due to conduit being so thin.

Nothing else fits but conduit fittings.
I've still got my 3/4" and 1" dies, but never had 3/4" or 1" taps otherwise I could have cut a locknut for you.

Note to yourself for the future, if you ever come across imperial conduit save some of the fittings for future use.

Thanks both. Every day's a school day...

 

[R-fur]

I think it was known as BET British electrical thread. See attached.

 

[suffolkspark]

Yes, it's a 100mA RCD. The client installed it - an ebay special - himself a while ago, when he realised there was no protection at all on the submain.

Has that cable got overload protection now somewhere or just that rcd between service fuse and the boards it serves

 

[happysteve]

Has that cable got overload protection now somewhere or just that rcd between service fuse and the boards it serves

No, and that's the problem, and that's why I'll be fitting a switch fuse before doing any work. I was there to do an EICR.

Current setup (TN-C-S):

Service head (BS1361, "80A" on label)
-> meter
-> 100A DP isolator
-> Henley block 1 (which also has outgoing tails to local DB1)
-> 16mm T&E (length about 2m)
-> 100mA RCD
-> exposed flex singles (length about 20cm, approx 16mm CSA)
-> another Henley block
-> MICC (length about 20-30m)
-> DB2 (adjacent/physically linked metal fuse boxes with BS3036 fuses)
-> socket circuits

Proposed setup:

Service head
-> meter
-> 100A DP isolator
-> Henley block (which also has outgoing tails to local DB1)
-> 25mm or 16mm tails
-> switch-fuse
-> MICC
-> new DB2 (with 30mA RCD protection for all circuits)

 

[happysteve]

For anyone interested, here's the before and after photos of both ends of this old pyro submain.

Was a shame to take out the old metal BS3036 boards (and the dual RCD board wasn't my choice, it was supplied by the client - normally I fit all-RCBO boards). The other end, however, was a big improvement.

Thanks for all the info and suggestions about the old imperial thread - a 1" to 25mm adapter worked a treat for the end that was missing a locking ring.

Cheers all!

DB2 before:

DB2 after:

Source of pyro distribution circuit, before:

Re-terminated using switch-fuse:

 

[MJPD29]

Looks a good job

 

[davesparks]

That's a creative way to misuse a thread adaptor.