UK Is the main fuse head satisfactory protection for SWA supply cable?

[Sparky09]

Commercial/Industrial installation. Summary of installation:

Main feeder pillar contains TNCS incoming supply single phase 100A main fuse, 25mm DNO tails, meter, 100A double pole isolator switch, 25mm tails/16mm CPC to 63A rotary isolator, 10mm SWA cable 25m run to digital advertising panel into a 100A double pole main switch.

Digital advertising panel DB contains 7x C10 RCBOs for the 7 sections of the screen wired in 1.5mm flex.

My question is as follows.. is the main fuse head satisfactory protection for that 10mm SWA cable? Or does it require a switched fuse isolator as it is over 3m in length? Furthermore should it have its own DB and the SWA on a 50A MCB due to the cable size being 10mm and in ducting underground which can only take a maximum of 58 amps.

As it stands that cable has a 63amp rotary isolator & a 100A DP switch before the isolator. Meaning the only protection it has is that 100A main fuse which assuming it actually has a 100A fuse inside doesn’t provide satisfactory overload protection for this cable size in the first place.

 

[littlespark]

No chance.

Needs fused down for change in cable size.


Why is there 2 x isolators? The 100A dp, and the rotary? Should the dp isolator be a circuit breaker, and been put in by mistake, or as a repair?

 

[brianmoooore]

Why is there 2 x isolators? The 100A dp, and the rotary? Should the dp isolator be a circuit breaker, and been put in by mistake, or as a repair?

Check that there isn't fuse or MCB tucked inside the case of either of these, especially the rotary isolator.
Total bodge, of course, but I've seen it done where space has been very limited.

 

[Sparky09]

No chance.

Needs fused down for change in cable size.


Why is there 2 x isolators? The 100A dp, and the rotary? Should the dp isolator be a circuit breaker, and been put in by mistake, or as a repair?

The 100A DP switch is pretty standard in these supply feeder pillars. Just a means of isolation for safe maintenance on the installation down the line. The 63A rotary isolator however is the part that seems pointless to me. I imagine it was just used a a point to terminate the SWA cable into. But if you’re going to go through the effort of terminating armoured cable into a small rotary isolator why not just put a small 4way CU in and terminate the SWA into a 50A MCB instead. The issue I have is I’m doing an EICR on this installation and I have to explain to the client why this isn’t satisfactory. As you can imagine the client is going to say it’s been fine for the last 5/10 years so why the sudden urgency now? As far as I’m concerned it’s black and white, the overload protection in the form of the 100A main fuse head isn’t doing anything for a 10mm cable.

 

[littlespark]

Just tell him it’s been unsatisfactory for 5/10 years…. It’s your report.

 

[Sparky09]

Just tell him it’s been unsatisfactory for 5/10 years…. It’s your report.

Just for arguments sake as I come across quite a lot of questionable installations in the digital advertising industry. Am I right in saying even if that cable was say 25mm SWA & the main fuse head was 100A it would still need either an MCB to protect that armoured cable or alternatively a switched fused isolator? Or would that main fuse head alone be sufficient protection for that armoured supply cable providing the fuse size was the correct rating for the cable size? Thanks

 

[Sparky09]

Check that there isn't fuse or MCB tucked inside the case of either of these, especially the rotary isolator.
Total bodge, of course, but I've seen it done where space has been very limited.

Nope no fuse or MCB located anywhere apart from of course the 100A main head. I would assume they’ve used the rotary isolator just as a means to connect the SWA cable instead of wiring it directly into the bottom of the DP switch. But I just don’t understand if you’re going through the effort of terminating an armoured cable into a rotary isolator why not just install a small CU with an MCB to make life easier and actually give the cable sufficient protection. The pillar works were very poor as a whole. Meter tails were terminated poorly with the outer sheath stripped back way too far. Originally it was 16mm tails and a 6mm earth as well.