50ma rcd.

[westward10]

So not much going on so I thought I would throw this out. On a periodic last week in a school we had two of the MK power tracks where you plug the sockets to them. Each track had an rcd enclosure with a 100ma, Wylex BS4293 rcd. The oddity is that the rcd enclosures have traffolyte labels fitted stating 50ma rcd, I thought nothing of it other than a 40 year old spelling mistake however when it came to testing them they tripped at half their rated current, 50ma in my eyes. There is no evidence of external additions, anyone had this before.

 

[Andy78]

What did it ramp test at ?

 

[westward10]

Didn't actually do a ramp test as my rcd tester is somewhat antiquated, none of the sockets were in use either.

 

[The Ghost]

Never seen anything like it in my life. So what do you do with that in your report? Is the 50ma sign valid? Never heard of an adjustable 100ma RCD, only 2000ma. Did you code it?

 

[westward10]

Have been pondering this didn't give it much thought at the time, even though there was no parts attached to the rcd it is possible there is something connected across the power track terminals. It is supplied from an MEM Exel board which has had an alternative neutral bar fitted in the top of the enclosure rendering it all but inaccessible with the neutrals randomly connected, some circuits had no IR tests this being one of them, maybe an IR test would have shown something.

 

[westward10]

Never seen anything like it in my life. So what do you do with that in your report? Is the 50ma sign valid? Never heard of an adjustable 100ma RCD, only 2000ma. Did you code it?

Yes I gave it a C3 stated it trips at half its rated current, no big deal really just a bit odd that it is identified as 50ma.

 

[The Ghost]

So where is the OCPD in that then, its usually 40a for powertrack? I think!

 

[Flanders]

Was it not a 500ma rcd , saying that though it should not of triped when tested,at 100ma

 

[westward10]

So where is the OCPD in that then, its usually 40a for powertrack? I think!

Is on a BS88,32A fuse.

 

[westward10]

Was it not a 500ma rcd , saying that though it should not of triped when tested,

Definately 100ma.

 

[Flanders]

Sorry never come across a 50 ma rcd , i wonder if they were specialy made by wylex for some school regulation and they used a 100ma enclsure ,

 

[westward10]

Sorry never come across a 50 ma rcd , i wonder if they were specialy made by wylex for some school regulation and they used a 100ma enclsure ,

The 100ma is on the rcd case, now I have thought about it am wondering if there is some resistors in the track terminal enclosure it is the only explanation.

 

[Dave OCD]

I've never heard of it either, once helped install a 5ma one as a young apprentice [around 1982] which had a huge transformer as part of it, really heavy. It supplied a hydrotherapy unit for disabled kids.

 

[The Ghost]

Or some coil device to up the PEFC.

 

[darksideby182]

Hampshire school science labs used to have the old big transformer type rcd protection at something silly like 2.5mA and when they upgraded the science labs they are now all on 10mA rcbo's , the amount of call outs i'd get week to week about stuff tripping on them.
I did find it odd that they would be put the gas taps , water tap and sink with sockets on, on islands around the classroom seems all abit close together.

 

[Deleted member 9648]

The 'old big transformer' units are Blakeley safety supply units. The centre tapped tranny halves the voltage to earth,but the voltage is on each pole, so a 13a socket will have both poles energised at 115v to earth and 230v between poles. Coupled with the 2.5-5ma RCD it was standard practice in school labs etc and many are still in service.
Because both poles are energised it is vital that all accessories are DP switches, something often overlooked when broken accessories are replaced creating a potential danger to users.