Fixed Appliance RCD Protection

[lozarus]

Afternoon - despite a recent 18th edition pass (all but one right!) I'm having a bit of a moment whilst planning some upcoming works at our site. In reality I should wait, go home, refer to the big book and go from there. But it's playing on my mind and I can be a bit impatient. Also, I guess there may be a bit of a conversation here about existing circuits?

Situation is as thus - need to provide a spur for sign installers to install a backlit sign - all 24v LED stuff - Class 2 transformer, connected to switched fused spur.

Unbelievably (but not altogether unexpectedly), when checking how the land lay, I found a live but unused spur floating around above the suspended ceiling - an old Ashley thing, complete with smashed backbox and a bit of tape on saying "Live" (this isn't unusual in an ex-public building that has had 60 years of various companies and sub-sub-subcontractors doing reactive 'maintenance' classed works with no real records left).

So, traced the FCU - fed in old colour FP200 from a mid 90's Federal board on its own B16 - old plans indicate it used to feed a former Fire Alarm system before it was decommissioned and replaced/relocated 20 years ago. No other appliances on circuit. Zs well within. IR not yet done.

So - do I need to protect any part of this circuit with an RCD? I deduce not, as its not a socket outlet upto 32a - its a fixed appliance. And the circuit itself already exists as installed.

My brain started going down this path because really, all I'm doing is connecting an appliance - the circuit itself is already in situ.

Appreciate there's options here and the obvious thing is to shove an RCD in- source an RCBO for the board; fit an RCD in a DIN enclosure; fit one of the much debated RCD spurs ....but does it really require one? (I can't really see the risk from the appliance perspective - it's more the fixed wiring - but as I say - that already exists).

Apologies for the musing of such a small thing - but just thought I'd throw it out there

 

[loz2754]

I see no particular reason for an RCD to be required in this situation.

 

[Pete999]

Afternoon - despite a recent 18th edition pass (all but one right!) I'm having a bit of a moment whilst planning some upcoming works at our site. In reality I should wait, go home, refer to the big book and go from there. But it's playing on my mind and I can be a bit impatient. Also, I guess there may be a bit of a conversation here about existing circuits?

Situation is as thus - need to provide a spur for sign installers to install a backlit sign - all 24v LED stuff - Class 2 transformer, connected to switched fused spur.

Unbelievably (but not altogether unexpectedly), when checking how the land lay, I found a live but unused spur floating around above the suspended ceiling - an old Ashley thing, complete with smashed backbox and a bit of tape on saying "Live" (this isn't unusual in an ex-public building that has had 60 years of various companies and sub-sub-subcontractors doing reactive 'maintenance' classed works with no real records left).

So, traced the FCU - fed in old colour FP200 from a mid 90's Federal board on its own B16 - old plans indicate it used to feed a former Fire Alarm system before it was decommissioned and replaced/relocated 20 years ago. No other appliances on circuit. Zs well within. IR not yet done.

So - do I need to protect any part of this circuit with an RCD? I deduce not, as its not a socket outlet upto 32a - its a fixed appliance. And the circuit itself already exists as installed.

My brain started going down this path because really, all I'm doing is connecting an appliance - the circuit itself is already in situ.

Appreciate there's options here and the obvious thing is to shove an RCD in- source an RCBO for the board; fit an RCD in a DIN enclosure; fit one of the much debated RCD spurs ....but does it really require one? (I can't really see the risk from the appliance perspective - it's more the fixed wiring - but as I say - that already exists).

Apologies for the musing of such a small thing - but just thought I'd throw it out there

After scrolling through all the answers, need to sort it yourself or get someone in who knows what they are doing, sort the situation out and make it safe, simple really if you are unsure get an expert t in PDQ.

 

[timhoward]

I think he knows what he is doing, and it probably is already safer as he's found the breaker.
My only thought is it would be good to improve on the "floating around on suspended ceiling".

 

[littlespark]

The instructions that come with the sign may include “must be connected to an RCD protected circuit”
If so, then the decision has been made for you.

 

[lozarus]

Sorry if I didn't make myself clear - I didn't mention anything about what I've done post finding this, as I felt the post made it incredibly obvious I'm actually qualified, competent and employed to do this job - as well as my previous contributions to the forum!

I mean if you get non-electrically competent people talking about Zs values and DIN enclosures then that's good stuff - but I thought it was clear im in the trade ?

I've obviously traced and isolated the circuit, I just didn't mention it as I assumed it was obvious I'm competent - I was just floating the idea about how I may go about reinstating it for an alternative use.

 

[lozarus]

The instructions that come with the sign may include “must be connected to an RCD protected circuit”
If so, then the decision has been made for you.

You make it sound so obvious !

 

[littlespark]

Unless the instructions are badly translated from Chinese, then it’s anyone’s guess

 

[ipf]

Presumably, it's not domestic and, as you say, it's not a socket outlet.....and I wouldn't think FP200 is in a wall less than 50mm, anyway.....is it?
From what you say, just replace the FCU and test.

 

[DefyG]

FP200 would have an earthed shielding too so RCD unnecessary unless as said installation instructions require one.

 

[lozarus]

Thanks all. Yes not domestic, FP200 above suspended ceiling. Will review instructions on arrival - it's a violently expensive thing made in England so fingers crossed with the instructions !

 

[loz2754]

FP200 would have an earthed shielding too so RCD unnecessary unless as said installation instructions require one.

Not so, see this post:
Post in thread 'Fire Alarm Circuit RCD Protection TT System' Fire Alarm Circuit RCD Protection TT System - https://www.electriciansforums.net/threads/fire-alarm-circuit-rcd-protection-tt-system.192171/post-1679373

 

[ipf]

FP200 would have an earthed shielding too so RCD unnecessary unless as said installation instructions require one.

Never heard that one. How do you earth that stuff?....except with a bear earth conductor maybe touching it.

 

[DefyG]

Prysmian cable spec - 'Features and Benefits' - 'Full size CPC in direct contact with screen'!

I wasn't suggesting using the screen as a cpc but know from its construction it will provide a pretty reliable earth path in event of a fault, and whilst it isn't specifically listed in 522.6.204(i), [The list isn't all inclusive], its use isn't prohibited and is compliant with 133.5.

 

[westward10]

FP200 Gold would require additional rcd protection in the eyes of BS7671.