AC mains and low voltage DC in same cable?

[rod]

Is it acceptable to use a spare core in a 4 core armoured cable to carry 12volts DC when other cores in the same cable are carrying AC mains?

 

[Darkwood]

I deal a lot with mixed cable voltages and induction is a big issue in my job, also there is the concern of a damage cable raising the voltage on the ELV side to LV levels which can be a fire risk if not a life risk... cables damage can be common and point 6 notes a earthed screening for this purpose in multicore cable otherwies why write it into the regs to start with as we have other regulations to deal with interference between cables.

 

[Ian1981]

Is it permissible to run ELV Ethernet over LV 230V ac cables?

Is the ELV Ethernet insulation rated the same as 230 v cables?
Then no

 

[Ian1981]

As I interpret it that is for the same wiring system, they have made a specific regulation exemption No' 6 for multicore cable as that does not fall under the term same wiring system due to the fact its a cable and not multiple cables or cores in a wiring system.

yep agreed I've re read it over and it does say system , I even wrote the dam thing on the thread.

 

[Ian1981]

This is interesting as I come across this a lot and never use the cable for ELV as worry about interference.......so you reckon there can't be an induced voltage due to the insulation Ian? Surely that can't be the case as you can get induced voltage from LV to LV? Or am I getting it wrong? Would be handy to be able to use the same cable for ELV and LV.

See further replies in the thread pal.
As Darkwood pointed out,
If the same cable used for containing both bands it needs to be as option 6 and have an earthed screen

 

[Deleted member 26818]

Is the ELV Ethernet insulation rated the same as 230 v cables?
Then no

I would assume so, as the conductors used for the Ethernet are the ones already being used for the 230V.

 

[Darkwood]

I would assume so, as the conductors used for the Ethernet are the ones already being used for the 230V.

LOL - your been a tad cheeky here, injecting a waveform signal into a cable been used is obviously not what is been discussed here and works off totally different technology

 

[Deleted member 26818]

Just wondering why there has to be screening between cores in some multicore cables, when it's possible to use the same cores for both ac and dc?

 

[davesparks]

How will you get induced voltage on the dc circuit if the cores are insulated to the highest voltage present i.e. 230volts?

Induction relies on the cores being insulated from one another, otherwise it wouldn't be an induced voltage, just a direct connection.

 

[Darkwood]

Just wondering why there has to be screening between cores in some multicore cables, when it's possible to use the same cores for both ac and dc?

It is probably because of the issues a fault could cause IE in a damaged cable, of that regulation the exception no' 6 specifically states Earth screening to the same level of the highest rating of the largest conductor thus implies it is been implemented as an earthed barrier, as it is discussing LV and ELV here (AC/DC) not actually been the issue then it comes down to a few factors, consider how DC or ELV AC is generated of our LV supply, it's common but not exclusive for it to have galvanic isolation, this would allow for potential dangerous voltages to exist on ELV gear without fusing, some of the cheaper DC motor controllers I use do not possess galvanic isolation and this leaves a floating voltage at LV level which can exist on the controls, not a issue until you start connection 0-10v speed controls on them and the user might have wet hands... I have to ensure I fit in a galvanic isolation unit in the circuit for user safety, the same principles could happen to a damaged cable carrying both LV and ELV without an earthed screen between them.

The crucial factor here is what the OP is connecting here, what the DC is for and how it is generated, it still doesn't give room for any excursions from the regulations although you could if it is shown to not be an issue of any kind, any regulation in the BS7671 is advisory although you need to ensure you have a lot of paperwork to justify any such breaches of regulations.

 

[Wilko]

As I interpret it that is for the same wiring system, they have made a specific regulation exemption No' 6 for multicore cable as that does not fall under the term same wiring system due to the fact its a cable and not multiple cables or cores in a wiring system.

Hi - I'm going to stick my neck for purposes of a good discussion, and not saying I'd like to run 12V in the same multicore cable as 400V .

Reg 528.1, intro says no mixing Band 1 and Band 2 unless one of the 6 exemptions applies. Understood. I take it on board about the 6th method, but if we read it as a specific method for multicore cable, what about the 2nd method? Where it also says "each conductor of a multicore cable". Doesn't that mean there are 2 exemption methods for multicore cable? I haven't spotted why 6 should be read as separate from a wiring system but 2 should not

 

[Ian1981]

Hi - I'm going to stick my neck for purposes of a good discussion, and not saying I'd like to run 12V in the same multicore cable as 400V .

Reg 528.1, intro says no mixing Band 1 and Band 2 unless one of the 6 exemptions applies. Understood. I take it on board about the 6th method, but if we read it as a specific method for multicore cable, what about the 2nd method? Where it also says "each conductor of a multicore cable". Doesn't that mean there are 2 exemption methods for multicore cable? I haven't spotted why 6 should be read as separate from a wiring system but 2 should not

It mentions wiring systems so if I read it again to me it's saying that if I have singles in conduit I can run band 1 and band 2 in the same conduit wiring system if each conductor is insulated to the highest voltage present i.e. 230 v.
Is a multicore cable then a wiring system in its self is the question?
If so then it's allowed
I'm kinda going back on forward on this one.
Anyone else?

 

[Ian1981]

Actually to me option 6 is saying if your cable isn't insulated against the highest voltage present on each conductor then that needs to be employed with earth screening.

 

[Darkwood]

Well in honesty I did say IMHO, yes I missed that part in point II @Wilko - and agree with both you and @Ian1981 on that.
I work on machinery to differing reg's and the reason for my take on this is safety under fault conditions, I see a big flaw in this regulation and I may raise it with the IET myself, but it would seem simply having the insulation value to the highest conductor would suffice, I would still consider the implications of the LV crossing over to the ELV and the potential risks associated with it if it were to occur, fusing alone isn't always a sufficient, like I said I said before, if DC is generated and isolated from the LV side in its generation then this could potentially create a accident waiting to happen.

 

[Darkwood]

With regards to wiring systems, usually by the nature of the wiring system you are afforded extra mechanical protection, be it trunking, conduit etc and as long as it is suitable for the environment then it should give a good serviceable life protecting the cables inside, a multi-core cable however could be just a flex and is more likely to be at risk from damage so I would argue that extra consideration be taken when choosing this method although the OP is discussing SWA so mechanical protection is somewhat afforded.

 

[Ian1981]

Well in honesty I did say IMHO, yes I missed that part in point II @Wilko - and agree with both you and @Ian1981 on that.
I work on machinery to differing reg's and the reason for my take on this is safety under fault conditions, I see a big flaw in this regulation and I may raise it with the IET myself, but it would seem simply having the insulation value to the highest conductor would suffice, I would still consider the implications of the LV crossing over to the ELV and the potential risks associated with it if it were to occur, fusing alone isn't always a sufficient, like I said I said before, if DC is generated and isolated from the LV side in its generation then this could potentially create a accident waiting to happen.

It's been a good discussion tho in which the forum is all about.
No name calling either