[Ian_m]

I am in the process of installing electric underfloor heating mat. The
installation checklist has fill in boxes box for heating element resistance,
probe resistance and insulation resistance both before and after
installation.

However the heating mat is double insulated (has only live and neutral
wires, though is screened) so how am I suppose to test the insulation
resistance. I can undertstand after fitting, testing between live/neutral
and earth as a check against accidental insulation damage, but before
installation ?

The form looks like a generic form and I suspect is wrong, the inulsation
resistance being for the mains wiring as opposed to the heating mat itself.

Any thoughts on what values I am looking for after installtion ? (n G Ohm?)

[fred]

In article , Ian_m
writes
I am in the process of installing electric underfloor heating mat. The
installation checklist has fill in boxes box for heating element resistance,
probe resistance and insulation resistance both before and after
installation.

However the heating mat is double insulated (has only live and neutral
wires, though is screened) so how am I suppose to test the insulation
resistance. I can undertstand after fitting, testing between live/neutral
and earth as a check against accidental insulation damage, but before
installation ?

In the uninstalled state it does appear to be a box ticking exercise, in your
place I would test between live, neutral and screen. The test should really
be done at working voltage or above to so that means a megger rather than
a multimeter, many things are insulators at low voltage but less so at
mains levels.

I think they are trying to avoid claims for failure after fitting, perhaps under
a screed, by requiring you to test before pouring.

The form looks like a generic form and I suspect is wrong, the inulsation
resistance being for the mains wiring as opposed to the heating mat itself.

Any thoughts on what values I am looking for after installtion ? (n G Ohm?)

Not my area of expertise but with plastic insulation I'd be concerned about
anything much below 20M.
--
fred
Plusnet - I hope you like vanilla

[[email protected]]

On 6 Mar, 15:57, "Ian_m" wrote:

I am in the process of installing electric underfloor heating mat. The
installation checklist has fill in boxes box for heating element resistance,
probe resistance and insulation resistance both before and after
installation.

However the heating mat is double insulated (has only live and neutral
wires, though is screened) so how am I suppose to test the insulation
resistance. I can undertstand after fitting, testing between live/neutral
and earth as a check against accidental insulation damage, but before
installation ?

The form looks like a generic form and I suspect is wrong, the inulsation
resistance being for the mains wiring as opposed to the heating mat itself.

Any thoughts on what values I am looking for after installtion ? (n G Ohm?)


I hope youre using paralleled elements, as individual elements are a
bit prone to failure. With parallel elements its a minor thing if one
dies.

I'm not sure theres any practical point testing L-E before pour, since
the insulation between L&E will be different once laid. As Fred said,
perhaps a deny-your-claims exercise. A visual or tactile check for
damage would be more useful.

Your min R will be in megs, not gigohms.


NT

[Ian Middleton]

On 6 Mar, 19:23, wrote:
On 6 Mar, 15:57, "Ian_m" wrote:

I am in the process of installing electric underfloor heating mat. The
installation checklist has fill in boxes box for heating element resistance,
probe resistance and insulation resistance both before and after
installation.

However the heating mat is double insulated (has only live and neutral
wires, though is screened) so how am I suppose to test the insulation
resistance. I can undertstand after fitting, testing between live/neutral
and earth as a check against accidental insulation damage, but before
installation ?

The form looks like a generic form and I suspect is wrong, the inulsation
resistance being for the mains wiring as opposed to the heating mat itself.

Any thoughts on what values I am looking for after installtion ? (n G Ohm?)

I hope youre using paralleled elements, as individual elements are a
bit prone to failure. With parallel elements its a minor thing if one
dies.

I'm not sure theres any practical point testing L-E before pour, since
the insulation between L&E will be different once laid. As Fred said,
perhaps a deny-your-claims exercise. A visual or tactile check for
damage would be more useful.

Your min R will be in megs, not gigohms.

NT

Ah ha. The earth wire has been found, it just started about 1-2"
further down the wire than the live and neutral. Interestingly the
wiring diagrams show a single black line connected to the thermostat,
not showing it is really 3 wires. Anyway L/N - earth measured at
greater than 50M both before and after instalation so all OK.

[Clive Mitchell]

In message .com, Ian
Middleton writes
Ah ha. The earth wire has been found, it just started about 1-2"
further down the wire than the live and neutral. Interestingly the
wiring diagrams show a single black line connected to the thermostat,
not showing it is really 3 wires. Anyway L/N - earth measured at
greater than 50M both before and after instalation so all OK.

If the earth wasn't in use before it might be worth checking it's
connected at the other end. In the hands of idiots I've seen the earth
core used as feed in a two way lighting arrangement. Never assume
anything. That's how you get electrocuted.

--
Clive Mitchell
http://www.bigclive.com

[Lurch]

On Tue, 6 Mar 2007 15:57:05 -0000, "Ian_m" mused:

I can undertstand after fitting, testing between live/neutral
and earth as a check against accidental insulation damage, but before
installation ?

You check before installation so you have a reference measurement.
--
Regards,
Stuart.

[Ian_m]

"Lurch" wrote in message
...
On Tue, 6 Mar 2007 15:57:05 -0000, "Ian_m" mused:

I can undertstand after fitting, testing between live/neutral
and earth as a check against accidental insulation damage, but before
installation ?

You check before installation so you have a reference measurement.
I have now have both a before and after reference measurement, both 20M.as
the test equipment I have has 0-20M and greater than 20M readings @ 500V.