1mm Twin earth cable query

[Dave Plowman (News)]

Presumably to differentiate from three phase?

Still rubbish though. ;-)

[nick smith]

OK - nit picker(s), in this context my point is ...

Is the 1.0mm cable being used for the 12 volt part of the circuit (if it exists) or the 240 volt part of the circuit. (cue someeone to correct me on 240 volts "not existing anymore")

My point (as most well knew) is that the current (at whatever the total load is) is going to be twenty times greater in a 12 volt circuit and the 1.0mm cable is unlikely going to be adequate, except for short runs and/or low power....

---------- Are we trying to help the OP or not ---------------

Nick

[Andy Wade]

No, 3-ph 400 V is still low voltage. LV is anything up to 1000 volts AC or 1.5 kV DC between conductors, or 600 V AC & 900 V DC to earth.

Not really, these voltage classes have been in use for decades. 11 kV (line) only counts as medium voltage.

It's context dependent. A 1.5 kV rail inside a piece of electronic equipment would probably be labelled 'EHT'. For electricity generation, distribution and supply it's only LV.

For line voltage (i.e. voltage between phases) in 3-ph distribution systems:

- LV is up to 1 kV

- MV is > 1 kV to 36 kV

- HV is > 36 kV to 245 kV

- EHV is > 245 kV

In BS 7671:

- ELV is up to 50 V AC or 120 V ripple-free DC, whether between conductors, or to earth

- ELV sources are either SELV (floating wrt ground) or PELV (earthed)

- LV is anything exceeding ELV up to the limits defined above.

[Pedge]

"nick smith" wrote in news:BYMId.51$ [e-mail]:

OK. Most of the plasterboard has gone up and the wiring i've done is as follows:

- Main wiring into kitchen from fusebox is 1.5mm

- Connected the 1.5mm cable to a junction box and used 3x 1.5mm wiring at

30cm lengths to connect to 3x 12v transformers which will supply 3x 50W Halogens.

The Emcalite transformer says that it is 240V - 11.4V, 50~60Hz, 20-60VA,

0.27A, SELV. I didn't actually mention in my original posting but I am using a dimmer switch for the halogens.

The second part to the wiring from the junction box installed is that a

1mm cable was conected to the neutral terminal and a red wire to the switch terminal. This will supply lighting to the kitchen wall units. I can see that some lights out there also use 12V tranformers.

I've tested each wire where the lights work.

[Mike]

UL (Underwriters Labs), the people who certify mains power supplies in most equipment, define the safe limit as 42volts

[Frank Erskine]

Not in the UK though.

[Mike]

UL is the main body recognised worldwide to make such definitions. What is different in the UK ?

In any case the IEC regs would override the UK ones even if they were different.

[Christian McArdle]

My main question is what do you mean here?

What is this 1mm red cable? Is it a single? Does it run alone? Care should be taken to avoid loops, where current takes a different path to its return. This can be avoided by using T&E and never having any loops in the system (i.e. different path for live than neutral).

This is normally done by wiring permanent mains (L+N) to a junction box and having a separate T&E cable to the light switch and then 3+E from there to subsequent switches. The light fitting(s) then come off on their own T&E cable. Sometimes (such as with pendant fittings) the junction box is included within the light fitting and it is called "loop in". However, the electrical layout is identical in both cases.

What should not be done is having a single cable run from permanent live to the switch and a separate single cable taking a different route to the junction box or light fitting. This leads to induction, which interferes with audio equipment, particularly hearing aids.

Running singles adjacent in conduit is close enough to T&E to be perfectly acceptable.

Christian.

[Andy Wade]

Err, the fact that we're in Europe, not North America. The legal framework for electrical product safety in EU countries comes from what is usually called the 'low-voltage directive' or LVD[1] which is implemented in the UK as the Electrical Equipment (Safety) Regulations

1994. These cover equipment operating at between 50 and 1000 V AC or 75 V and 1.5 kV DC, which matches the definition in BS 7671. Compliance with the regulations can be demonstrated by product manufacturers by the use of harmonised European standards - such as EN 60950 (IT equipment) and EN 60065 (A/V equipment) EN 60335 ('white goods' type appliances) - not UL standards.

(It is true though that many UL standards are recognised worldwide, particularly UL 94 which deals with the flammability of materials.)

The IEC makes standards, not regulations.

[1] Directive 73/23/EEC, full title: "Council Directive of 19 February 1973 on the harmonisation of the laws of Member States relating to Electrical Equipment designed for use within certain voltage limits." This was one of the first EEC directives to be implemented in the UK, and was modified in 1994 to require CE marking.