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?

 

[Zdb]

I wouldn't.

 

[Taylortwocities]

Read the regs! 528 (ish)

For a multicord cable... the cores of a band I circuit (eg 12v DC) should be separated by an earthed metal screen of equivalent current-carrying capacity to that of the largest core of a Band II circuit.

So, in a regular SWA cable, No.

 

[freddo]

As above, but it is permitted if the ELV is part of a control circuit for the LV, and the supplies are part of the same system. There are loads of SY and YY cables around that contain LV power and ELV control in the came cable. It's certainly not permitted to power a socket with some cores and 12V lighting with the others for example.

 

[Taylortwocities]

True. It's allowed in interlinked smoke alarm wiring. Line, neutral and (what is probably) an ELV connection as the interlink.

I'd worry too about the 0v reference for the 12v DC conductor. Is he thinking of using the mains earth

 

[freddo]

Oh yea I read core as cores!

 

[Ian1981]

As long as every conductor is insulated to the highest voltage present i.e. 230 v then it is allowed to have a dc and ac voltage together
See below

 

[Ian1981]

Except where one of the following methods is adopted, neither a voltage Band I nor a voltage Band II circuit shall be contained in the same wiring system as a circuit of nominal voltage exceeding that of low voltage, and a Band I circuit shall not be contained in the same wiring system as a Band 2 circuit except where

1. (i) Every cable or conductor is insulated for the highest voltage present
2. (ii) Each conductor of a multicore cable is insulated for the highest voltage present in the cable
3. (iii) The cables are insulated for their system voltage and installed in a separate compartment of a cable ducting or cable trunking system
4. (iv) The cables are installed on a cable tray system where physical separation is provided by a partition
5. (v) A separate conduit, trunking or ducting system is employed
6. (vi) For a multicore cable, the cores of the Band I circuit are separated from the cores of the Band II circuit by an earthed metal screen of equivalent current-carrying capacity to that of the largest core of a Band II circuit

 

[Strima]

You will also have to take into account harmonic effects from the AC and quite possibly induced voltage on the DC circuit.

 

[Ian1981]

You will also have to take into account harmonic effects from the AC and quite possibly induced voltage on the DC circuit.

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

 

[Hellmooth]

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.

 

[Darkwood]

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

Insulation rating does not effect induction, however as the OP is discussing a multicore cable then to comply like you and others have put it has to have a earthed screening which will block any chance of an induced current between the 2 categories as we must assume AC mains means 230/400 volt ac against his 12v DC, as for harmonics, if you suspect this as an issue then the wiring and preventative measures in total needs careful design.

 

[Ian1981]

Insulation rating does not effect induction, however as the OP is discussing a multicore cable then to comply like you and others have put it has to have a earthed screening which will block any chance of an induced current between the 2 categories as we must assume AC mains means 230/400 volt ac against his 12v DC, as for harmonics, if you suspect this as an issue then the wiring and preventative measures in total needs careful design.

Band 1 (ELV) and Band 11 (LV) circuits can be contained in the same cable where each conductor of a multicore cable is insulated to the highest voltage present i.e the Band 11 voltage
alternatively this is allowed where the cores of the Band 1 circuit are seperated by an earthed metal screen of equivelant current-carrying capacity to that of the largest core of the Band 11 circuit
As stated in option 2 I listed given in bs 7671
It's how I interpreted it

 

[Darkwood]

Band 1 (ELV) and Band 11 (LV) circuits can be contained in the same cable where each conductor of a multicore cable is insulated to the highest voltage present i.e the Band 11 voltage
As stated in option 2 given in bs 7671

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.

 

[Deleted member 26818]

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

 

[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.