RCD Protection for CCTV

Question

Hi all, 
 
 I have a question if RCD's are required for 230v CCTV Cameras. 
 
 1. It is a TT system, resistance values unknown and not tested. 
 2. CCTV is fed from a 6A (MCB), SP&N DB, directly to a PSU which sits above the metallic camera column 
 3. Load is around 1A 
 4. Cable is 2.5mm singles within the metallic camera column, therefore daggling inside it. 
 
 Question is: do I require an RCD? Lightening protection has been risk assessed out, as it it not needed. If there is a break in the mains cable feeding the PSU, do I require an RCD? Resistance values from two points are less than 50ohms. Unfortunately an earth mat cannot be installed or electrode. 
 The client has also requested a CPC to the metallic column, but the main cables are protected. Is this the same principal as earthing a metallic back box within a domestic installation? I have looked at the BS761 regs for the answer, and I'm guessing as it's LV it may be required? 
 
 Please can someone advise?

AJJewsbury · Accepted Answer

Generally if you have LV (e.g. 230V) live conductors only covered with single insulation that, if the insulation broke down for whatever reason, could energise an exposed conductive part, then the part needs earthing and you need to arrange things to provide automatic disconnection of supply (ADS) in the case of a fault to such an earthed part, or indeed to the c.p.c. of the circuit. On TN system, where fault currents are reliably high, a fuse or MCB will typically disconnect adequately quickly. On a TT system that less likely to be the case. If the earth loop impedance is 50&Omega; say, 230V will only generate about 4.6A - so a 6A MCB is unlikely to trip at all. Normally for TT some kind of RCD (not necessarily a 30mA one) will be needed - not only for the equipment itself, but usually for the circuit(s) supplying it too. That need not necessarily be per-circuit - it was common enough in the old days to have a single RCD "up-front" covering an entire installation, or as an incomer for a distribution board (often a 100mA or more, time delayed). If it is a TT installation, there should be some means of providing ADS for all the parts upstream too. 
 30mA RCDs for "additional protection" are a different matter (although the same device may be used for both additional protection and ADS in some cases) - depending on the circumstances (e.g. location and if the circuit supplies certain other types of equipment) such protection might be required, but probably not if it's just for CCTV. 
 - Andy.

gkenyon · Answer

Heera said: I have a question if RCD's are required for 230v CCTV Cameras. 
 The design should be conducted by someone who is competent and experienced with the particular location(s) in which the cameras are being installed, especially if members of the public can access the column. From your description of the earthing arrangements, an RCD appears likely to be needed for automatic disconnection of supply according to Chapter 41 of BS 7671, although knowledge of the 'resistance values' that are 'unknown and untested' would be necessary to complete the design in any case. There are also cases in which BS 7671 requires additional protection by 30 mA RCD for safety (e.g. Regulation 411.3.4 for installations associated with dwellings, Section 714 for outdoor lighting and street furniture accessible to the public). The designer might also choose this for safety, after considering safety of the installation according to relevant legislation.

AJJewsbury · Answer

Except if it's street furniture or similar that comes under Section 714 ? 
 
 I did think of that, but my reading of 714 seems to suggest additional protection is only required for lighting (714.411.3.4). I take the point that the risks are likely similar (although the most similar, a street lighting column, is specifically excluded from the requirement), and of course the designer is always free to go beyond minimum BS 7671 requirements if good judgement requires. 
 - Andy.

Sergio Fernandez · Answer

Have you tried PoE (Power Over Ethernet) CCTV camera, the caveats are in the length of cable but you could 230v nominal to the control panel which is more secure or in a controlled area and then PoE from the control cab to the camera which negate a lot of things like RCD and other safety precautions. Once on PoE you could add battery backup power in case it is needed.

gkenyon · Answer

AJJewsbury said: but probably not if it's just for CCTV. 
 Except if it's street furniture or similar that comes under Section 714 ? I wouldn't want to be the one that decided to leave out additional protection for a CCTV column accessible to the public (even if on private land) after this tragic case: www.bbc.co.uk/.../uk-england-london-56758749

RCD Protection for CCTV

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