Rcbo's

[cliffed]

Just finished installing power sockets in It suites at a school.
All protected by 30 ma rcbo's ,circuits specified by electrical consultants,15 2 gang skts on each circuit.All working & no trip outs.
My reckoning was about 7 2 gang skts per circuit,what's your feelings on this.
Have I gotta change my reasoning on these circuits & follow suit.

 

[Deleted member 72666]

That's far more than I would dare to put on each rcbo, out of interest how many cct's did you install?

 

[Deleted member 72666]

Oh, and were the circuits rings or radials?

 

[Leesparkykent]

I normally follow a rule of thumb of no more than 8 computers/work stations per circuit.

 

[Andy78]

A good idea would be to measure the actual earth leakage on the circuits with all sockets in use. I would be interested to know the results.

I used to do a lot of IT room installs for a previous company and the local authority spec was 6 double sockets per 32A ring circuit. This was based on one workstation (one pc and one monitor) per double outlet. I always thought this was a bit on the cautious side.

 

[cliffed]

Oh, and were the circuits rings or radials?

Ring main circuits,2 for each classroom,6 classrooms in total.In each room total of 30 2 gang sockets.

 

[Deleted member 72666]

Ring main circuits,2 for each classroom,6 classrooms in total

Were they all fed from the same dist. board and if so how did you accommodate all the cpc's given that they have to be kept seperate?

 

[Martin Kerr]

Why are you so concerned ?, just follow the consultants design ,that's what he is getting paid for.
Just sign the installation section of the cert

 

[Pete999]

Oh, and were the circuits rings or radials?

Beat me to it Mate

 

[Pete999]

Were they all fed from the same dist. board and if so how did you accommodate all the cpc's given that they have to be kept seperate?

Pardon, kept separate?

 

[Leesparkykent]

Pardon, kept separate?

High integrity earthing so the cpc's will be in separate terminals in each socket and in the DB.

 

[Deleted member 72666]

Cpc's for high protective conductors currents.

 

[Deleted member 72666]

Thanks Lee!

 

[Pete999]

High integrity earthing so the cpc's will be in separate terminals in each socket and in the DB.

Right so how is that going to be a problem?

 

[Deleted member 72666]

Depending on the size of board and number of circuits you can find yourself fast running out of earth terminals.
.... And it throws them out of sync when every other terminal is in the correct termination number wise.

 

[cliffed]

Depending on the size of board and number of circuits you can find yourself fast running out of earth terminals.
.... And it throws them out of sync when every other terminal is in the correct termination number wise.

Not a problem using 18 way TPN DB,all earths connected correctly for installation

 

[Leesparkykent]

Right so how is that going to be a problem?

Its not really if the boards big enough you just end up with loads of spare ways that cant be used.

 

[Pete999]

Depending on the size of board and number of circuits you can find yourself fast running out of earth terminals.
.... And it throws them out of sync when every other terminal is in the correct termination number wise.

Carp just take your time jobs a good un, two earth terminals at the DB for either a Ring or Radial final circuit nothing difficult or out of the ordinary for a good Sparky, although it doesn't apply to the Domestic Installers.

 

[Deleted member 72666]

Not a problem using 18 way TPN DB,all earths connected correctly for installation

I recently did a small(ish) office which had amongst other things 3 radial cct's with high integrity earthing fed from a 10 way single phase board. I installed an extra earth bar to accommodate the extra cpc's but didn't use it in the end as I found a different way of doing it and still achieve compliance with the regs.

 

[Martin Kerr]

I think this is where the Regs trips it self up in situations like this, apart from a few additional terminals for main earths, bonding etc, no standard DB can fulfill the requirements for high integratity earthing comprising more than a couple of circuits and unless the additional earth conductors are cable I'd, it would make it very confusing for the next person coming along at a later date.

 

[Deleted member 9648]

In one of our school sites there are some IT suites with more PC's than the OP's spec on each RFC. Not sure on exact numbers but I suspect there are as many as 15-20 PC's on some,which run without problems. One large suite had around 20-30 PC's running from a dedicated DB with a 30ma main switch....cant recall it ever tripping.

 

[cliffed]

Yea no probs connecting cpc's & numbering them, the hassle were connecting the corresponding earths of the rcbo's.Reckon another seperate earth bar would be the answer.

 

[Deleted member 72666]

I think this is where the Regs trips it self up in situations like this, apart from a few additional terminals for main earths, bonding etc, no standard DB can fulfill the requirements for high integratity earthing comprising more than a couple of circuits and unless the additional earth conductors are cable I'd, it would make it very confusing for the next person coming along at a later date.

Exactly!
I always use cable markers (partek ones I find the best) but still think some clown who next comes along to add a circuit or two will bugger it up and just connect them together even though there's a label warning them of the setup.

 

[Trevle]

Surely there wouldn't be a problem with say circuit 4 - lights sharing the no.4 earth terminal with circuit 2 - ring? If you're running out of terminal, just as long as the two from the ring aren't in the same terminal.

 

[Pete999]

Its not really if the boards big enough you just end up with loads of spare ways that cant be used.

If you are saying that then, you must be installing a lot of high integrity circuits, then at the the planning stage you should have taken the need for extra earth bars into account.
Realistically how many circuits with the need for HI earthing would be required in, say a small to medium sized office installation, more to the point how may Electricians do you know who actually employ this method, I was involved in a recent EICR as an adviser where the RFCs where just chucked in, no notice taken of the possible earth leakage possibilities.

 

[Deleted member 72666]

Yea no probs connecting cpc's & numbering them, the hassle were connecting the corresponding earths of the rcbo's.Reckon another seperate earth bar would be the answer.

I agree fully! When I asked you the questions I wasn't trying to be 'picky' I just wanted to know what everyone else does.

 

[Deleted member 72666]

In one of our school sites there are some IT suites with more PC's than the OP's spec on each RFC. Not sure on exact numbers but I suspect there are as many as 15-20 PC's on some,which run without problems. One large suite had around 20-30 PC's running from a dedicated DB with a 30ma main switch....cant recall it ever tripping.

Ha, ha, ha, I'd have been back to test the rcd when they were next on holiday!

 

[Flanders]

About 15 years ago we were guided 8 twin sockets not just due to earth leakage but due to the start up of those old monitors now we all use lcd which use a lot less power , i dont knowif the old monitors produced any earth leakage but i would of thought the lcd one don't produce any . And as said if as been designed for 15 sockets then thats down to the designer to worry about. Maybe pcs dont produce as much earth leakage as they did in the past .

 

[cliffed]

Very true,maybe it's the way forward .

 

[Martin Kerr]

Send an an RFI to the consultant ,asking how he would like to comply with the relevant regulation based on his DB selection?

 

[Pete999]

As long as you wire the circuits, be they Rings or Radials correctly as per OSG 7.5 and adhere to the rules therin, as well as OSG 6.15 you should be OK

 

[Martin Kerr]

As long as you wire the circuits, be they Rings or Radials correctly as per OSG 7.5 and adhere to the rules therin, as well as OSG 6.15 you should be OK

Can you refresh my memory to these points Pete, I Think the dog eat my copy ,few years back

 

[Pete999]

Can you refresh my memory to these points Pete, I Think the dog eat my copy ,few years back

Well 7.5 shows you how to wire the circuits and the reasons and 6.15 shows you what labels are required, nothing earth shattering (excuse the pun)

 

[cliffed]

What do you mean

 

[cliffed]

Send an an RFI to the consultant ,asking how he would like to comply with the relevant regulation based on his DB selection?

What do you mean?

 

[cliffed]

Thanks guys for the answer for above

 

[Martin Kerr]

If the number of earth terminals supplied within the DB , is not sufficient to comply with the recommendation of the high integrity earthing .ask him how he would like them terminated?

 

[Pete999]

If the number of earth terminals supplied within the DB , is not sufficient to comply with the recommendation of the high integrity earthing .ask him how he would like them terminated?

If you have to ask him that question then he aint done his sums right.

 

[Martin Kerr]

Well 7.5 shows you how to wire the circuits and the reasons and 6.15 shows you what labels are required, nothing earth shattering (excuse the pun)

Don't go spilling any of that red wine over the OSG Pete

 

[Pete999]

Don't go spilling any of that red wine over the OSG Pete

All gone Martin she rations me now

 

[Sintra]

Handy little PDF on the subject. http://electrical.------.org/wiring-matters/26/5437-earthing.cfm?type=pdf

 

[Martin Kerr]

All gone Martin she rations me now

What about the hip flask in the the sock?

 

[Pete999]

What about the hip flask in the the sock?

Been married over 40 years Martin she knows all the hiding places it just aint worth it, should have put my foot down early on but anything for an easy, stress free life

 

[Martin Kerr]

All gone Martin she rations me now

Sounds like she is one with a bit of sense

 

[Martin Kerr]

Been married over 40 years Martin she knows all the hiding places it just aint worth it, should have put my foot down early on but anything for an easy, stress free life

Bet you can hide an odd twenty?when its your round

 

[shanky887614]

A good idea would be to measure the actual earth leakage on the circuits with all sockets in use. I would be interested to know the results.

I used to do a lot of IT room installs for a previous company and the local authority spec was 6 double sockets per 32A ring circuit. This was based on one workstation (one pc and one monitor) per double outlet. I always thought this was a bit on the cautious side.

that seems cautious, i might rig up a temp socket with my pc later to check