Rewirable fuses and the old wylex boards

[baldsparkies]

Sorry Tony, but another just as independant elderly person could have replaced the original fuse wire with an oversized piece of cable.
Created a house fire and die due to smoke inhalation.
No not a theoretical situation. THIS REALLY HAPPENED.
So NOW where do the rewirables fit in ????????
Glad you wouldnt go back to them though mate.
Honestly I would outlaw the ruddy things. Just wait and see, amendment bla bla bla, will come along, and the old rewirable supporters will suddenly be saying. You HAVE to change them, says so in the regs book.

 

[hillbillie]

I changed a TP&N rewirable board last week. I failed it as it was about 3-4 metres from the transformer and had a Ze of 0.00 ohms (well, at least according to my Fluke) and the Zs of the three circuits on it barely had any more (readable) resistance. It just fed the sockets and lights in the switch room. The 25mm 4 core feeding it is currently fused at (3X) 60A BS88s, which I will upgrade to 100A soon. Now, I remember reading in GN3 that you had some leeway with the short circuit capacity of BS3871 and later kit if there was a BS88 upstream but not for BS3036 fuses. So I decided that the fuses weren't up to the PFC it could receive and that was my justification.

I replaced with a Hager 4 way and have used it for the fire and burglar alarm supplies, the lights and sockets in the switch room and have put two 40A triples in which I will use to feed another couple of d/bs next month.

However, The old 3036 d/b (a MEM I think) was much sturdier than the flimsy Hager I replaced it with. Solid iron!

 

[nickblake]

Just to chuck a rock in your pool. A major disadvantage of the MCB is the ease it can be repeatedly reset by an elderly person.

A very good friend of mine (an industrial spark) fitted 60898’s in his mother’s house. The house had been re-wired to the as then current 15[SUP]th[/SUP] edition. He then went to work abroad leaving the message with mum, any problems get in touch with Tony, (I was only around the corner).

So the MCB for the immersion tripped, mother being one of those independent types reset it. It instantly tripped, she reset it again, and again, , , , , , , , , , Eventually the hot water cylinder exploded.

Had it been wire she would have had to give me a call. Plus saved me a lot of work repairing the house, Doug, her son was in China at the time so was a bit stuck as to helping out.

New isn’t always the best.

No I wouldn't go back to rewireables..... But.

did have an old chap wrap fuse wire round his fuse in a rewirable and a fuse in a plug top blew a hole in the base of a metalic standard lamp and took out a fuse at the substation one lucky guy way prefer mcb's

 

[ipf]

did have an old chap wrap fuse wire round his fuse in a rewirable and a fuse in a plug top blew a hole in the base of a metalic standard lamp and took out a fuse at the substation one lucky guy way prefer mcb's

Blimey, must have been a fair bit of fusewire !

 

[baldsparkies]

Blimey, must have been a fair bit of fusewire !

I have seen a bit of stripped back 2.5 chucked in the ruddy things on more than one occasion.
One instance was a busy pub. And the guy that did it was the landlords hero. Why?? because he got the bars chillers pumps and lights going of course. Ring main plus 2 lighting circuits. all in the same way.
Why was I called out. Well there was a funny fishy smell coming from the board, not that anyone was worried of course, they were all well tanked up by then.

 

[ipf]

Seen it myself mate, double wrapped round the pins of HRC fuse carriers and asking why the motor's burnt out. No sign of any overloads and god knows how there was no fire.

 

[IQ Electrical]

I changed a TP&N rewirable board last week. I failed it as it was about 3-4 metres from the transformer and had a Ze of 0.00 ohms (well, at least according to my Fluke) and the Zs of the three circuits on it barely had any more (readable) resistance. It just fed the sockets and lights in the switch room. The 25mm 4 core feeding it is currently fused at (3X) 60A BS88s, which I will upgrade to 100A soon. Now, I remember reading in GN3 that you had some leeway with the short circuit capacity of BS3871 and later kit if there was a BS88 upstream but not for BS3036 fuses. So I decided that the fuses weren't up to the PFC it could receive and that was my justification.

I replaced with a Hager 4 way and have used it for the fire and burglar alarm supplies, the lights and sockets in the switch room and have put two 40A triples in which I will use to feed another couple of d/bs next month.

However, The old 3036 d/b (a MEM I think) was much sturdier than the flimsy Hager I replaced it with. Solid iron!

The UK Anex that you mention for upstream protection was actually written with BS3036 fuses in mind, allowing the UK to continue using them.

 

[Engineer54]

I changed a TP&N rewirable board last week. I failed it as it was about 3-4 metres from the transformer and had a Ze of 0.00 ohms (well, at least according to my Fluke) and the Zs of the three circuits on it barely had any more (readable) resistance. It just fed the sockets and lights in the switch room. The 25mm 4 core feeding it is currently fused at (3X) 60A BS88s, which I will upgrade to 100A soon. Now, I remember reading in GN3 that you had some leeway with the short circuit capacity of BS3871 and later kit if there was a BS88 upstream but not for BS3036 fuses. So I decided that the fuses weren't up to the PFC it could receive and that was my justification.

I replaced with a Hager 4 way and have used it for the fire and burglar alarm supplies, the lights and sockets in the switch room and have put two 40A triples in which I will use to feed another couple of d/bs next month.

However, The old 3036 d/b (a MEM I think) was much sturdier than the flimsy Hager I replaced it with. Solid iron!

As a matter of interest, what is the size of the TX or TX's that's feeding this main switchboard, and what KA rating has the Hager DB MCCB and MCB's have??

 

[Knobhead]

A good point E54! I would be very dubious about this set up.

 

[nickblake]

Blimey, must have been a fair bit of fusewire !

30 amp wrapped round the fuse in the plug top and around the rewirable fuse in the CDU think it was 4 times round each

 

[hillbillie]

As a matter of interest, what is the size of the TX or TX's that's feeding this main switchboard, and what KA rating has the Hager DB MCCB and MCB's have??

A good point E54! I would be very dubious about this set up.

Now you've got me worried.

Engineer 54, you queried me stating this was a PME system in another thread and you have got me thinking.

I don't know the characteristics of the transformer. I have just called the DNO and they want me to e-mail them with my request, which I will do so shortly.

The premises used to be a factory and needed a lot more power than it currently does. The place is currently used as a warehouse and apart from the roller shutters and a 3 phase socket, it needs power for lights and sockets (and an immersion heater).

I said it was a PME system because this is written on a crimped off panel in the switch room. However, there are three and a half cores (seven cables) and an earth cable going back from the switch room to the transformer. This is beyond my knowledge but if I hadn't have seen 'Protected multiple earths' on the panel under the MCCB I would have assumed it was a TN-S system.

The d/b I replaced was used for the lights and socket in the switch room, I suppose the switch room got its own dedicated way so that electricians could still work there when the other d/bs and busbars were switched off.

The power supply to the fire alarm was, until I changed it, a 30A isolator with 1.5mm singles going back to a d/b, the line being wrapped around a screw on a busbar! Fused at 200A! I decided to run the power supply back to the switch room so that there was minimal chance of the fire alarm power supply being tripped somewhere else.

Now to the board I put in. The switch room unit has a 1600A MCCB and several busbars and d/bs coming from this fused at 315A for the busbars and 200A/160A/63A for the d/bs (all BS88s). The board I replaced has a 25mm 4 core fused at 3X63A. I did not put a MCCB on it, I used a 125A switch. Is this wrong? I used 10KA mcbs, this was the highest I could get.

When calculating diversity, I thought that the 63A BS88 fuses (and 100A fuses later if I change them) would not go before the mcbs on the Hager, looking at their respective curves. Consequently the fire alarm power supply and any sub board I feed from it would not be tripped by something else on the board.

Please let me know if you've seen any errors.

 

[Engineer54]

Let's just look at this installation as if it were still for a factory. As there is a distribution TX that is supplying this factory, the earthing arrangement for the TX would in almost all instances serve as the main earthing for the installation covered by the TX. It is very unusual to have a PME earthing arrangement, on a TX supplied factory premises, it is always TN-S!!

So i don't quite understand why you have a panel there stating PME. Is this TX now under the control of the DNO, and supplying distribution networks outside of the factory?? This is the only thing i can think of at the moment, that would make any sense as to why your installation at present is a PME connection. ...ie, you are now just a small user being fed from a DNO distribution network that has been PME'd for DNO network distribution strings outside of the once factory boundaries.

As for the rewirable DB you have just upgraded to a MCB DB, the BS88 fuses should clear any KA fault current, but i still prefer to use high KA breaking MCBs when that close to the source TX. By the way, if the Main breaker to this installation is 1600A, it sounds like you have a 1000KVA TX. Assuming a reactance of 5% the TX could be capable of delivering a SCC of as much as 20MVA into a fault.

EDIT... We use all MG/Schneider protective devices which cover just about any circumstance you can find. They manufacture 22KA range of MCBs ,which is what we use in and around sub-stations, that incorporate TX's... We also always incorporate MCCB's in final circuit DB's rather than the normal isolators, mainly to confine any tripping to the panel, rather than tripping in distant boards/panels...

One more thing that is worth mentioning, it is quite normal to make the TX main N-E connection at the main switchboard rather than at the TX itself. So maybe, this is what they are calling PME, which it isn't, not in the true sense of word, it's the main Neutral earthing point. Maybe they ran out of the correct sticker notices?? lol!!

 

[Engineer54]

Hillbillie,

Any chance of you taking a few photo's of your main switchboard, the PME labelled panel and if possible the TX itself?? I'd be very interested to see what your working with here.
Thanks in advance... lol!!!

 

[Engineer54]

The UK Anex that you mention for upstream protection was actually written with BS3036 fuses in mind, allowing the UK to continue using them.

That's probably right IQ, but still a bit silly using BS3036 fuses in a sub room 3 or 4 meters from what in all likelihood is a 1000KVA TX!! At least install a HRC cartridge fuse board in those circumstances!! lol!!!

 

[hillbillie]

So i don't quite understand why you have a panel there stating PME. Is this TX now under the control of the DNO, and supplying distribution networks outside of the factory?? This is the only thing i can think of at the moment, that would make any sense as to why your installation at present is a PME connection. ...ie, you are now just a small user being fed from a DNO distribution network that has been PME'd for DNO network distribution strings outside of the once factory boundaries.

One more thing that is worth mentioning, it is quite normal to make the TX main N-E connection at the main switchboard rather than at the TX itself. So maybe, this is what they are calling PME, which it isn't, not in the true sense of word, it's the main Neutral earthing point. Maybe they ran out of the correct sticker notices?? lol!!

This must be the case. The transformer is the DNOs property and is padlocked off and only accessible via the back door. I've never seen it. I don't have the knowledge needed to understand transformer neutral earthing points but the green and yellow single I mention seems to come from the transformer and up to what is used as the MET, bolts on top of each section of the panels connected together with more 50mm (I think) green and yellow single...heading up to the structural steel. This doesn't seem to go near the back of the panel marked PME but I haven't had a look since December.

As for the rewirable DB you have just upgraded to a MCB DB, the BS88 fuses should clear any KA fault current, but i still prefer to use high KA breaking MCBs when that close to the source TX. By the way, if the Main breaker to this installation is 1600A, it sounds like you have a 1000KVA TX. Assuming a reactance of 5% the TX could be capable of delivering a SCC of as much as 20MVA into a fault.

EDIT... We use all MG/Schneider protective devices which cover just about any circumstance you can find. They manufacture 22KA range of MCBs ,which is what we use in and around sub-stations, that incorporate TX's... We also always incorporate MCCB's in final circuit DB's rather than the normal isolators, mainly to confine any tripping to the panel, rather than tripping in distant boards/panels...

20MVA! That should turn those BS88s to glass pretty quick! I thought about putting in an MCCB as the d/b switch but thought that this would cause a bit of a headache re diversity i.e. having to go from 63/100A BS88s to an MCCB and then the mcbs. I thought that the switch would accept anything the 63A BS88s and even 100A BS88s would let through temporarily.

However, there is a good chance that I will be putting another d/b next to it in February or March, from another 100A way in the switchboard, I'll try to find the schneider switchgear you mentioned. My local retailer doesn't sell it but I'm sure I can find the stuff on the internet somewhere.

Any chance of you taking a few photo's of your main switchboard, the PME labelled panel and if possible the TX itself?? I'd be very interested to see what your working with here.

Certainly. I have some photos of the switchboard on this computer and I can take a photo of the PME labeled panel next week. I'll upload the photos I have in this post:


Lastly, many thanks for your wisdom!