MICC gland thread

I'm guessing this is one for the older chaps....

Got a job we are involved with at the moment, switchgear upgrades in a school built in '71. The submain between one end and the other is 4no single core 50mm pyros in a duct.

Original panel has been correctly slotted between the gland holes, however the locknuts used on the glands are the standard galv steel type thats magnetic so not really right (though its been wrong for 50 years). Ideally want to change them to brass. The glands were ID'd as 1H50 on the side, had a bit of googling found it was going to be 25mm and forseeing this issue ordered M25 brass locknuts.

The guy came to put them on, and they looked like it would fit, but they got almost onto the gland but they were just a tiny bit too small to start threading on, the original nuts go on fine. Now I'd generally at this point suspect that they are imperial sized and probably 1" BSW....but...... an imperial thread on a gland intended for a metric sized cable, could that even be a thing?

I get at in '71 the metric changever was happening, there are some 4 core MICCs in the same panel that are imperial sized, and thers even a ring that leaves board as 2.5/1 and returns as 7-029/3-036 but both systems on the same gland... I'm doubtful, buyt what else could it be.

If it is, where does one get 1" BSW brass locknuts from, the wholesaler I use for 'tricky' stuff quoted me a 4week lead time and 40 locknut minimum (its the lead time thats the killer). googing brings up plumbing fittings, but if I think BSP is different to BSW, with the sizing being to the internal bore of the pipe its intended to be used with, rather than the size of the thread

have you tried the old lock-nuts on a new 25mm thread?
25mm and 1" are very close in size(0.4mm i think) and sometime fit

Any chance of slotting the old nuts and then brazing the slot up.? Not ideal,but it may work. Fiddly bit of filling for the threads tough.
Have you tried that MICC company , I think in Hull or Newcastle called something like Pi-Rho?


Or get a local amateur lathe fiddler to thread a piece of brass tube and part off 4 'rings' for you?

kerching said:

Have you tried that MICC company , I think in Hull or Newcastle called something like Pi-Rho?

Click to expand...

Sorry, have you got a link, I've tried googling and it only finds some sort of investment consultancy firm!

Brazed up slot sounds a good idea, but I am not really set up to do it, I doubt I'd braze something like that with my mapp torch!

The having them turned sounds a good idea, I did ask a enginneering firm but was told the cost would likely be prohibitive, could try and find a bloke in shed... but I guess not many people would have a 1" BSP tap..... (and I'm guessing its 1" BSP I need)

I did think of trying to get hold of a tap and run it through the 25mm locknuts, I know it wouldn't have the full strength as effectivly two threads overlaid, but should have enough to do what it needs to be, its not like its to hold Aircraft Windows in

https://www.ebay.co.uk/itm/37246327...ar=641269837665&widget_ver=artemis&media=COPY
Are these no good?

I think BSP is different to BSW https://www.stevensonplumbing.co.uk/bspt.html being sized to the diametrr of pipes they are intended for, rather than the actual diameter. That said the 3/4BSP does look just a smiden over 1" o/D however its 14tpi instead of 8tpi for the BSW which I expect would make it difficult to get on even for a locknut that only spans maybe 2 threads? :s

metric fitting should have a small cut on each corner , does the gland have cuts like this

I think it's this

https://thermal-resources.com/contact-us/
They may be able to tellyou the thread size, if nothing else

As for runnng a tap through...try to get a cast blank plug, file an asymmetric V into the leading edge so,that it makes a sort of "tap"

@Phoenix the threads are to BS31, they are not BSW/F or P, or any UN.
1” conduit is 16 threads to inch, tpi.
So it’s special to conduit.

Conduit thread is a thread all on its own designed specially for conduit. How does any electrician not know this????

Anyway, here are conduit taps..
http://www.gjhall.co.uk/tool/bs-conduit-taps

And here is set of metric conduit thread dies [i have this set myself..

https://www.voelkel-shop.com/en/ele...BL218cxSYu45RSM2R6-za00N1mPtutvIaAjA7EALw_wcB

Sidewinder said:

@Phoenix the threads are to BS31, they are not BSW/F or P, or any UN.
1” conduit is 16 threads to inch, tpi.
So it’s special to conduit.

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Thanks, for some reason I got it into my head that it was standard whitworth, you don't happen to know why it seems that a gland for a metric MICC cable appears to have an imperial thread... did such things happen around the changeover to metric (Of course, not implying that you are old enough to have been on the tools back then....)

And A87..... Sorry, I just assumed they'd be to a standard thread used for everything else, like the M threads today (or is that not the case at all)

I may have a 1" x 16 TPI conduit tap
I know I have some 7L1.5 glands. Which are 25mm
If I have the tap,I can try one against for comparison, if you want?

If you could try to gently without forcing it to cut, put a 25mm locknut on the end of the tap, to see if the situation I have is replicated, the locknut should start to drop onto the thread, but there should be no way to get even one turn on it.

No problem
I've made a note to look for it in the morning
I know I have a 5/8" one, and a Rj Hall 20mm hand retheader

Just looked, sorry it's a 3/4" x 16tpi

The problem is even with Metric, threads have different pitches which can be a real pain!!