Maximum OCPD for SSSO

[SUNRAY]

I've had a very quick skim through my 2008 regs and not found the answer.

Today I've been out to resolve some findings on an inspection, this is a small industrial unit with remote cutout, 1ph meter, 80A fuse and 80A RCD. The feed cable is 35mm² 4 core SWA to this type

of 100A TP&N with bolted lug terminations in a small recess just inside the front door and from there a 25mm² 2 core SWA into the main area to the DB. Also there are 2 metal FCU's for intruder and fire alarms coupled to the box and fed directly from the load side with 2.5 or possibly 4.0mm² singles, accordingly they don't leave the confines or the metal enclosure.

The report (written by the same person for the previous 2 inspections) is now stating it needs an OCPD between the isolator and FCU's.
Because of the way everything is mounted in the confined space

it's gointg to be difficult to make changes.

Is there anything in 7671 or 1363 stating a maximum supply rating for 1363 accessories or for that matter others views?

 

[Murdochcat]

Not convinced of the need for additional fusing or MCBing down .........

 

[plugwash]

Whats the prospective fault current like? doing some googling it seems a BS1362 fuse has a 6KA breaking capacity.

 

[flameport]

Is there anything in 7671 or 1363 stating a maximum supply rating for 1363 accessories

Nothing.

Overload protection is provided by the fuse in the FCU or plug.

Fault protection would have to be determined, in that the combination of the disconnection time and short circuit current at the accessory would have to be low enough to not damage the supply cables if a fault occurred.
However using some generic values for 80A fuses, the minimum conductor size is far below 4mm², so unlikely to be any problem there.

 

[Adam_151]

Come across this a few times, I'm not aware of anything that says it can't be done, but I've never been been keen on it, given the ease that one can trap a cable in a metalclad fusespur when screwing it back, or on some makes when pulling it forward depending on placement of terminals. Its alright that the adiabatic says that the conductors will be alight, but I don't fancy a 100A fuse sized flash as I'm screwing a spur back. Yes, of course anyone doing this will be isolating the supply before opening it.....

Its allowed, but its its not sensible.

I think I might be tempted to label it up in such a way that even an intruder alarm engineer can understand that its backed up by something bigger than they'd normally expect in the hope that they would not try and unscrew it.

If you wanted to fuse it down, then SLYDLOK / GEC redspot carrier fitted in the isolator?

 

[SUNRAY]

Thanks for the replies, it seems the consensus is similar to mine, "should be fine but doesn't feel right".

Whats the prospective fault current like? doing some googling it seems a BS1362 fuse has a 6KA breaking capacity.

That I hadn't considered and I think will be the killer. There is a 1MW sub feeding the estate and maybe 8m parallel feed to the meter panel the 8 singles are about 30mm∅ so I'd guess 185 or 240mm² (370 - 480) and 30m of 35mm² to the isolator so my gut feeling is something a decent bit more than 6KA

Come across this a few times, I'm not aware of anything that says it can't be done, but I've never been been keen on it, given the ease that one can trap a cable in a metalclad fusespur when screwing it back, or on some makes when pulling it forward depending on placement of terminals. Its alright that the adiabatic says that the conductors will be alight, but I don't fancy a 100A fuse sized flash as I'm screwing a spur back. Yes, of course anyone doing this will be isolating the supply before opening it.....

Its allowed, but its its not sensible.

I think I might be tempted to label it up in such a way that even an intruder alarm engineer can understand that its backed up by something bigger than they'd normally expect in the hope that they would not try and unscrew it.

If you wanted to fuse it down, then SLYDLOK / GEC redspot carrier fitted in the isolator?

Funny you should say that, in my toolbag was a Redspot, I think a 16A fuse and there is even a convenient M4 tapped hole and I'd offered it up to the position and it didn't require a second screw to stop it turning as it would be tight up against a step.
Somehow it felt like a botch so didn't do it.

 

[333rocky333]

Do you remember SLYDLOK fuses we used to fit them inside isolaters etc to fuse down when needed

 

[SUNRAY]

Do you remember SLYDLOK fuses we used to fit them inside isolaters etc to fuse down when needed

I do remember them, but having not knowingly seen any for maybe 40 years I assumed they have vanished off the scene. I've used loads of redspots

with BS88's and as mentioned happened to have one with me. Actually I lie, what I had with me is a Bussman

I'm back there next week so I'll get a label made and fit one be done with it.