Pc Room

[gdog]

Hi there, do any members know how many pcs a 32 amp breaker would take? I looked at a pc suite which is being put together with a final ring circuit in dado trunking which has 14 socket outlets wired in 2.5 t&e. I would think this may trip the breaker if all pcs and monitors were running at full load. Also would 4mm cable not be more suitable? It's about a 30 meter run from db to the suite which is 5m X 5m

 

[Andy™]

depends how much power the PC uses. as for cable size, thats down to your cable & circuit design. and you do know about high integrity earthing, dont you?

 

[ProDave]

How many do you expect? How many will actually fit in?

Let's guess at one pc and one monitor per double socket, so 14 workstations.

Let's also guess at ordinary office pc's so say 400W for pc and monitor (not high end gaming machines)

So that's 5.6KW

Do you think that would bother a normal ring final on a 32A MCB?

 

[gdog]

Don't know about high integrity earthing Andy.

 

[Andy™]

you might want to have a look through 543.7.1...

 

[gdog]

ProDave, I agree that wouldn't affect a 32amp final ring. I assumed pcs and monitors would be more thirsty than that though. Thanks for your replies folks.

 

[Phoenix]

I wouldn't have thought running current would be an issue at all:

Issues would generally be:

The need for high integrity earthing

Likely hood of tripping 30mA RCD protection

Inrush current, upon power on that many PCs will certainly take out a B32, and quite possibly a C32 as well

 

[gdog]

Sorry about my ignorance on this matter folks. I have just looked up some info on 573.7.1 on line as I don't have a BS7671 to hand. Are normal pc's and monitors designed to have current flow through the cpc? If so how much?

From the limited amount I have just read would a separate cpc have to be run to each socket? Also should the equipment be connected to fused connection units rather than socket outlets and how would this reduce the chance of the rcbo tripping?

Thanks.

 

[Andy™]

depends entirely on the PC, but roughly 3mA per PC. no need to fused spur for PC's, but may need it for data racks etc

as for the earths, depends if you wire it as ring or radial

 

[steptoe]

you cant reduce the chance of the RCBO/RCD tripping if your leakage current gets too high,

the only way is to limit the number of appliances fed,

a rule of thumb for me is 8 appliances per circuit, ie, 4 d/skts

 

[gdog]

Oh dear. So with 14 pc's the circuit will definitely trip. Andy, would running a separate cpc to each socket in a ring alleviate this problem? Thanks

 

[steptoe]

Oh dear. So with 14 pc's the circuit will definitely trip. Andy, would running a separate cpc to each socket in a ring alleviate this problem? Thanks

NO

you still have the same accumulative leakage

 

[Andy™]

high integrity earths is NOT a solution to stop RCDs etc tripping. it will not lower the earth leakage.

its all in 7671 for what earths you need and where. 543.7.2.201 (i) if you have a ring, 543.7.2.201(ii) if you have a radial

 

[gdog]

Ok thanks guys.

 

[Steve3948]

Do you need RCD protection  :innocent