RCDs / MCBs for smoothed clean IT power supply

[getonline]

Keeping it short and simple.

Does anyone know of any products RCDs/MCBs that would be suitable for fitting in a CU for a ring supply to an office/computer room in a domestic environment?.

Presently looking at the possibility of a clean earth for this supply, any advice on this avenue? I have heard its a nightmare! TT as opposed to TNS / TNC-S.

Other suggestions have been using a twinned earth.

Max load 32A, will need to be B rated breakers I know.

Looking to protect against spikes/surges, brown-outs etc.
Rather than buy a post terminal surge protector, looking to protect the whole dedicated ring.

Only IT equipment will be drawing on this ring.

Any suggestions

Thanking you in advance

Garry

 

[JohnD]

MCBs and RCDs do not provide this protection.

For power cuts and brownouts (rare in the UK) you need a UPS. You may find one with spike and surge supression.

You may need to use shielded cables to prevent them picking up noise or EMP after the cable has emerged from the protective device. Or tempest-shield the room if you have the money and inclination. This is a specialised field which I am not experienced in.

For spikes, pulses and surges MEM for example make a variety of TVSS devices, including some which fit in a CU or DB to protect a single circuit (say, 32A). The bigger ones cost hundreds of pounds and upwards. I suppose that if you are not fortunate enough to have a MEM CU, there might be one available for the brand you do have; or you could assemble a small enclosure adjacent to the CU or DB. MEM make a lot of Industrial and Commercial equipment, and the SP devices are interchangeable between the industrial Memshield 2 and the domestic/light commercial Memera 2000 and 2000AD, so this makes devices available for domestic use that most manufacturers of domestic devices would not make.

Part no SS40 for example for a single circuit. You need one for each pole, so two for a single phase circuit and four for a three-phase circuit. They are coloured red.

Part no. SS15RR

You can look up, or phone for, the tech info. 08700 540 333 or
http://www.memonline.com/
http://www.memonline.com/f05.html

Of course, you need to protect the circuit with an MCB or RCBO as well.

 

[Paul Barker]

Not to mention the high leakage current environment, and the additional protective measures you are taking also create leakage current so you might actually need to look at not using an rcd as it is counter intuitive.

 

[Adam_151]

I think whoever mentioned dual earths was a tad confused (or you've mis-understood them)

But while the issue has been brought up:- if you are intending to supply a quantity of IT equipment then the cumulative protective conductor currents could foreseeably become more than 10ma, which means that you ought to invoke section 607 (high integrity earthing) which involves redundant earth paths incase one somehow goes open circuit (so that the system remains double fault to danger). If you are using a ring final circuit, you are very nearly there, just ensure you use outlets that have two earthing points on the earth bar (not to be confused with the ones that have a separate protective earth and a 'clean' one for the pins), and make sure the two cpcs go in separate terminals, same applies back at the DB. If using a radial circuit, make the cpcs into a ring by running 4mm² back from the last socket back to the DB, and remember the thing about separate terminals still applies, if you have two such radial circuits then you may as well kill two birds with one stone and put the 4mm² between the furthest points on both instead of back to the DB. Try and stay away from branched radials, they complicate matters.

 

[getonline]

Adam -
Thanks for that slant on things, was just going to use 2.5mm cable, but the 4.0mm is always a bandit to work with in my opinion. As for connection of the 2 earths, you suggest terminating them in different terminals at the CU?, One on the RCD side of the split load and one on the MCB, or does it not matter?

JohnD -
Thanks chap, MEM are the dogs cahunnas, but like you say, PRICEY!.
Came across this "clean power supply" unit on CPC. Thinking of positioning it externally of the CU, but running it from an MCB instead of an RCD, taking on board Paul Barkers comments
http://cpc.farnell.com/jsp/level5/module.jsp?moduleId=cpc/261091.xml

Don't want to go over board on this project (££££!), but now have food for thought, and more questions for myself from the answers you have given.

Cheers All

Garry

 

[ColJack]

by seperate earth terminals he just meant under 2 different screws on the one bar.. this ensures that one earth is still good even in the other screw comes loose..

in large installs we ofter mix the rings on the earth terminal.. ( IE ring 1 and ring 2.. in earth 1 we have 1 earth from ring 1 and one from ring 2, same in earth 2.. )

 

[RF Lighting]

What about installing filtered sockets?

clicky