The blasé attitude to mixing different voltage bands in the same duct was not useful.
Advice for underground cables
- Thread starter Jon-uk
- Start date
Sponsored Links
They may indeed.
If so then the cable manufacturers' specs will say.
If so then the cable manufacturers' specs will say.
- Joined
- 17 Aug 2010
- Messages
- 2,742
- Reaction score
- 453
- Country
I have such duct come up inside buildings or sheds. It is easier than it sounds and deals with all kinds of issues.
Sponsored Links
Why is it, I wonder, that it is considered safe for a person to touch the outside of an insulated and sheathed cable carrying 230V (maybe whilst in contact with something 'earthed'), but that there is perceived to be a potential (safety?) problem if it comes in contact with another insulated and sheathed cable (which may not be specced as 'insulated to 230V') connected to ELV circuits?
Rather than any safety issue, I think a good reason for keeping 230V AC and ELV cables 'apart' is the fact that the latter will commonly be used for signalling, control, comms or audio puposes, which may be susceptible to inference from 50Hz fields.
Kind regards, John
Maybe because any faults or breakdowns will only affect the poor sod touching the cable, whereas an ELV circuit becoming 230V could cause much worse mayhem.
I don't find that argument at all convincing.
Furthermore, the only situations I can think of in which the conductors within two insulated+sheathed cables could come into contact are ones in which the fact that ELV circuits might not like 230V would probably be the least of one's worries!
In addition to that, as we have discussed before, I strongly suspect that cables intended for ELV use are not specced/'rated' for 230V purely because they are not tested at that voltage. As I've said, I would imagine that, even if one wanted to, it would be quite challenging to manufacture a PVC/PVC cable that could not withstand 230V. I have personally not come across such a cable with does not IR fine at 1000V.
Kind Regards, John
Engineer at a transmitter site. Transmitter has failed. 230 volts on both legs of the incoming private wire from the control room.
The destroyed line isolation transformer in the TX made him aware there was something seriously wrong on the private wire.
Either a cable duct fire or a damaged amplifier cabinet, can't recall which was the cause of that incident
The latter would presumably be irrelevant to this discussion.
As for a cable duct fire, the result you describe would surely have been just as likely (i.e. equally unlikely!) had the ELV cable had insulation 'rated' at 230V - so I still don't really understand the thinking behind the regulation.
Kind Regards, John
Would you intentionally allow bell wire to come into contact with bare metal carrying 230 volts AC ?
Without a catch all regulation about the separation of LV and ELV cabling it would be considered by some non thinkers as "acceptable" for paper insulated ELV cables to be in close proximity / contact with exposed metal 230 volts terminals. So far safe but then not safe if the atmosphere is humid and the paper insultation is damp.
It is on the aftermath of a cable duct / cable tunnel fire when insulation has melted / been carbonised and water / foam has filled the ducts that ELV comductors can be affected by 230 volts from damaged LV cables.
Whatever the cause it became good practice to measure voltage on private wires relative to ground before touching them.
You have rather moved the goalposts - that's three layers of non-conductive barriers between the two conductors than we have been talking about (with two insulated+sheathed cables). Having said that, I think the chances of their being any problem would be extremely small.
What is this "paper-insulated ELV cable"?
In any event, as I've said, if it is considered safe to touch the outside of the insulated+sheathed LV cable, and if it is considered safe for the outside of that cable to come in contact with, say, earthed metal, then I don't really see what the perceived problem is.
Yes, I understand that, but my point remains - the regulation requires 'separation' of LV and ELV cables only if the latter does not have insulation 'rated' for the LV voltage concerned. If the ELV cable does have such insulation, then the regulations allow the two cables to be in contact. Once the insulation had melted and carbonised, the fact that it was 'rated' for 230V is hardly relevant!
Kind Regards, John
I do think the point John raises is worth consideration, I for one regard ELV mixed in with twin and earths as non-compliant and shouldn't be done, but unlikely to present a danger unless something goes seriously wrong... like the cable duct fire, the interference aspect should be enough reason not to do it, however.
ELV in a trunking containing a load of 6491X conductors is a much more serious issue and likely to attract a C2 on an EICR, especially considering a lot of containment systems may contain poorly made crimped and connector blocked joints!
I recently had to discourage a client's IT dept from trying to put a fibre link in the lighting trunking, put me on the spot a bit for a second or two...
ELV in a trunking containing a load of 6491X conductors is a much more serious issue and likely to attract a C2 on an EICR, especially considering a lot of containment systems may contain poorly made crimped and connector blocked joints!
I recently had to discourage a client's IT dept from trying to put a fibre link in the lighting trunking, put me on the spot a bit for a second or two...
Try google. Power cable and telephone cables have and, for some applications, still do use paper as the insulation next to the conductors.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
