LV and signal cores in the same sheath

[John D v2.0]

Hi all, I've just bought an Airflow Duplexvent DV72 ventilator made in UK and CE marked and I came to wire the unit into the mains.

I then discovered that the colours for L/N/E are red, black, green, which I was slightly surprised. Then I realised that the 6 core cable also included 0v and 10v output, and a proportional control core designed to vary fan speed via an external potentiometer or PWM controller.

Maybe I'm confused, but how can they combine lv and signal into the same cable with only insulation separating the cores? Have they just faked the testing or is this special magic cable?

 

[bernardgreen]

Provided the insulation between cores is capable of working at 230 volts ( mimimum 500v DC test amd preferable 1.5 kV flash test.) then there is nothing wrong with ELV and LV being in the same cable if the ELV is derived from the unit and does not connect to anything with a different 230 volt supply.

 

[John D v2.0]

So I should just IR test the cable and not worry about it.
I'm tempted to replace the wire anyway to reduce the chance of a wiring error as it's only screw terminals on a PCB.

 

[winston1]

Red, black, and green have not been allowed to be sold for many years. Contact trading standards.

 

[JohnW2]

Red, black, and green have not been allowed to be sold for many years. Contact trading standards.

Not, under normal circumstances, as a 3-core cable. However, this is a 6-core cable (hence three other colours as well), the manufacturer of the equipment having chosen to use red/black/green for the LV supply. I very much doubt that there is anything about the 6-core cable, per se, which would be of any interest to Trading Standards, but the way in which the manufacturer of the equipment has chosen to use it may possibly warrant some questions - although I suspect that there were/are 'no better' colours available than the ones they used.

Kind Regards, John

 

[bernardgreen]

although I suspect that there were/are 'no better' colours available than the ones they used.

If there are to be a lot of the units sold then the manufacturer could have had a bespoke cable laid up. Even a quantity as small as 1000 metres can be cost effective.

 

[JohnW2]

If there are to be a lot of the units sold then the manufacturer could have had a bespoke cable laid up. Even a quantity as small as 1000 metres can be cost effective.

What do you mean by 'cost-effective'? Surely not as cheap as (let alone cheaper than) an off-the-shelf cable?

Kind Regards, John

 

[Echo the husky]

Those colours are the same as US 240V colours, Black L1 Red L2 Green earth.

 

[winston1]

Those colours are the same as US 240V colours, Black L1 Red L2 Green earth.

Interesting. Didn't know that.

 

[securespark]

Red, black, and green have not been allowed to be sold for many years. Contact trading standards.

FFS. Are you bored?

 

[bernardgreen]

What do you mean by 'cost-effective'? Surely not as cheap as (let alone cheaper than) an off-the-shelf cable?

The savings come when, for example for a radio transmitter, there are two power cores at 4 amps, 5 signal cores at a few mA, and a twisted pair carrying modulation. Using a bespoke cable made it possible to have a single plug for all the connections rather that 3 separate cables, 3 plugs on the cables and 3 sockets on the control unit.

In the fan example that the OP mentions savings would be small and be from reduced copper in the signal conductors and less insulation on them provided the 230 volt conductors had adequate insulation.

 

[JohnW2]

The savings come when, for example for a radio transmitter, there are two power cores at 4 amps, 5 signal cores at a few mA, and a twisted pair carrying modulation. Using a bespoke cable made it possible to have a single plug for all the connections rather that 3 separate cables, 3 plugs on the cables and 3 sockets on the control unit.

OK, but it's only the twisted pair (which the OP doesn't need) that makes that partially relevant to the type of cable. If it weren't for the twisted pair, one could use a single off-the-shelf cable, with just a single plug/socket.

In the fan example that the OP mentions savings would be small and be from reduced copper in the signal conductors and less insulation on them provided the 230 volt conductors had adequate insulation.

The copper saving would not just be small but extremely small, and I'm sure would not make a bespoke cable 'cost effective', particularly since I imagine the OP only needs a metre or three. As for the insulation, I'm apart from my BYB at present, but I seem to recall that there is a requirement (one might say 'irrational') for all the conductors to have insulation adequate for the highest voltage present in any of the conductors.

Kind Regards, John

 

[bernardgreen]

particularly since I imagine the OP only needs a metre or three. As for the insulation,

I was thinking more of the manufacturer using a better cable.

If the ELV in the cable is derived from the LV in the cable using a power supply in a item of equipment and connects only to devices powered by the ELV then the insulation on the lower voltage conductors can have insualtion suited to the ELV.

It was only a suggestion that the manufacturer may achieve some savings.

 

[JohnW2]

If the ELV in the cable is derived from the LV in the cable using a power supply in a item of equipment and connects only to devices powered by the ELV then the insulation on the lower voltage conductors can have insualtion suited to the ELV.

Where does that come from? I've now been reunited with my BYB and, per my recollection, 528.1(ii) seems to be fairly clear in saying "Each conductor of a multicore cable is insulated for the highest voltage present in the cable", with any apparent qualifications such as you suggest.

As I said, it's arguably not a particularly rational a requirement, but that seems to be what it is.

Kind Regards, John

 

[bernardgreen]

From the people who made bespoke cables for interconnection of modules in a system.