high integrity board

[tbs1983]

I'm wiring a ring main into a room in a house that is being converted to an office with Dado trunking. The guy has several computers and loads of IT equipment therefore I'm weary of putting it on an RCD due to the earth leakage.
Im changing the CU also so ive ordered a high integrity board with the intention of keeping the office ring off the RCD's.

My question is can I get away with fitting a 32A MCB as it is a specialist circuit used by a competent person (despite the cable run being <50mm in wall). Or should I fit an RCBO?
just worried an RCBO will nuisance trip with all the IT equipment on it.

 

[Guest55]

i dont think you can apply the no rcd needed get out clause for a domestic dwelling circuit even if used as a place of work.
put office on dedicated circuit & rcbo.
problem solved.
on average a computer will kick out 4-6mA of earth leakage so youll still get 4 computers on a circuit before the 30mA rcbo finally trips out.

 

[Richard Burns]

If the office is in a house you cannot really get away with no RCD on sockets, also the subsurface cable would need RCD protection.
If you are putting in a new board run multiple radials on RCBOs for the office so that the load (and the leakage) is spread out.


Too slow!

 

[tbs1983]

cheers guys, Cables already wired for a ring but might take your advice and change it to 2 x 16A radials on RCBO's

 

[7029 dave]

If you go the radial route, correct me if I'm wrong you will have to beef up the cpc,if left on ring no need.

 

[brucelee]

and the sockets will be used for general use by ordinary persons and less than 50mm from surface then a 30mA RCD or better still its own RCBO as biff says or do as richard says and use radials with individual rcbos

and where socket outlets are likely to exceed 10mA earth leakage then use High integrity protective conductors pg 78 and 79 OSG for ring final or radial circuits then radials would be best if loads of IT equipment

 

[GLENNSPARK]

i dont think you can apply the no rcd needed get out clause for a domestic dwelling circuit even if used as a place of work.
put office on dedicated circuit & rcbo.
problem solved.
on average a computer will kick out 4-6mA of earth leakage so youll still get 4 computers on a circuit before the 30mA rcbo finally trips out.

what a load of old bullshyte this is...

to the O/P:

as long as the cable is within containment (surface run)..such as a trunking drop down to the compartmental stuff....
and the outlets are clearly identified...
then crack on....

 

[Darkwood]

Consider protection with SI units then computer leakage is a reduced issue as it ignores the designed leakage and still afford RCD protection ... If not i wouldn't really recommend having no RCD protection on sockets in a house as they generally get used for anything .... and its mainly for the buried <50mm so if you can avoid the depth issue then fit T -earthpin non standard sockets so they can only be use used for the items with the correct plugs on and identify as such.

The only let up on rcd protection in domestic now is for dedicated circuits of special consideration .... I.E. a kidney dialysis Machine or other such situe's where the chance of nuisance tripping could create a greater risk to life than the protection it.

If it is as suggested just home use and 1 computer set up don't worry about it .... ill disagree with the average leakage of a computer as i would say a max of 6 computers per 30mA rcd .... and double for a SI unit (3mA average per computer is what i learnt)

 

[CrazyScozzese]

Split the ring into 2 x 20 amp radials on RCBOs, but leave the CPC of both connected together. Meets regs, covers ars. Perhaps as old boys say you coud omit RCD but why bother, leave a smaller blame footprint.

 

[Darkwood]

If the circuit was considered to have a high enough leakage to be classed as a functional earth then no you can't do the above solution. OP needs to expand on the set up more to comment further.

 

[Engineer54]

Bit off subject here, but the only high integrity CU that i recognise as ''High Integrity'' is an ALL RCBO CU. How anyone can consider a CU with dual RCD's and a couple of unprotected ways as high integrity, i just don't know!!

As darkwood states, 3mA is the general rule for PC computers and other desktop IT equipment, unless known to be higher...

 

[kingeri]

I install a lot of wiring for IT equipment for the local council, now they insist on RCD protection we always limit the number of PCs per circuit to five.

 

[ahtyrrell]

I think it would be worth finding out exactly what's going to be in there, as IT equipment other then computers in a domestic sense such as routers, printers, scanners etc even laptops. are normally all class II equipment so have no leakage, its only the computers them selves that may have abit and to be honest I have had 5 or 6 in my house on the same circuit along with allsorts of other things with no tripping issues. So unless he is going to have more then 4 or 5 DESKTOP PCs then I wouldn't worry to much.

 

[Guest55]

what a load of old bullshyte this is...

What is bull ?
the regulation itself or my comment / interpretation of it ?

 

[Darkwood]

I think it would be worth finding out exactly what's going to be in there, as IT equipment other then computers in a domestic sense such as routers, printers, scanners etc even laptops. are normally all class II equipment so have no leakage, its only the computers them selves that may have abit and to be honest I have had 5 or 6 in my house on the same circuit along with allsorts of other things with no tripping issues. So unless he is going to have more then 4 or 5 DESKTOP PCs then I wouldn't worry to much.

Think your mistaken here... the items you have suggested are double insulated are more likely to be SELV where the power plug is the transformer ... this is where the leakage will be generated... Laptops also have a 230v plug with inline DC power supply ... any equipment that externally or internally converts mains AC to DC with smoothing circuitry like computers etc will probably be a source of designed earth leakage.

Where the nature of the DC output dosn't have to be so clean then yes they may be class II like phone chargers where its only used for charging the battery as oppose to running the device.

 

[Pete999]

Don't forget if you have more than 10ma leakage (think that's the correct value it's in the OSG anyway) you have to connect the cpcs (if it's a RFC) separate terminals on the cu, and use socket outlets with two earth terminals if it's a radal the the same applies to the sockets and you need to make the cpc a ring. It's all very clear in the OSG but mine is at work and I;m chillin out.

 

[GLENNSPARK]

What is bull ?
the regulation itself or my comment / interpretation of it ?

theres no requirement for RCDs in trunking surface run for specific outlets clearly marked/labeled as such...

 

[ahtyrrell]

Think your mistaken here... the items you have suggested are double insulated are more likely to be SELV where the power plug is the transformer ... this is where the leakage will be generated... Laptops also have a 230v plug with inline DC power supply ... any equipment that externally or internally converts mains AC to DC with smoothing circuitry like computers etc will probably be a source of designed earth leakage.

Where the nature of the DC output dosn't have to be so clean then yes they may be class II like phone chargers where its only used for charging the battery as oppose to running the device.

I take your point, but as an example I have two printers several Routers/Hubs all with A plastic earth pin also all 5 laptops I have (2 dell 3 Toshiba) all have figure 8 leads on them, although IIRC one of my old ones did have a 3 pin lead to the PSU. I cant actually find any pieces of IT equipment other then the desktop PCs that have an earth pin, not saying that its typical of all IT equipment particularly commercial stuff such as large printers and switches which obviously do generate leakage however in a domestic environment I would be surprised if leakage from IT equipment is ever really a problem

 

[Taylortwocities]

Surface cabling
RCD sockets
Job done