Retrofit insulation and older house wiring thermal considerations

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blindnz

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#293916 22-Feb-2022 08:37

Reaching out to see if anyone has come up against this?

I've recently pulled the Gib and I am retrofitting insulation into the all cavities (internal and external) for heat and noise reasons.

On the side of the pink batts it has a caution for electrical wiring pre 1989 as it may overheat, but makes no reference on what to do in any of the install guides. Rather most of these recommend fitting the insulation close and tight to the wiring. In some online guides people split the batts and run the wire through the batt and in others they tuck behind.

The house I'm renovating has older TPS cable which is in good condition. I understand that it can halve the current carrying capacity by 50% if the wiring is surrounded by insulation.

To get around this I'm not sure if I should run the wiring through conduit, notch the batts or do nothing. Anyone dealt with this before?

timmmay

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#2872584 22-Feb-2022 11:55

I suggest you talk to your electrician about this, rather than rely on advice online. For example, maybe it makes sense to rewire while the gib is off - I have no idea because I'm not an electrician.

Bung

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#2872601 22-Feb-2022 12:28

While it may take an electrician on site to give specific information advice from people like @gregmcc can be useful in helping frame the questions you ask.

rphenix

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#2872620 22-Feb-2022 12:51

I believe this is what your interested in reading up on. Agree with timmmay now is a great time to get an Electrician in also consider if you need RCD's on the circuits, or extra power points. I would jump on builderscrack and ask for a quote for a checkup.

Having done a few renovations with friends I've seen quite a few 'shockers'. Ive seen at least one example of:

Redundant live wires.
Electrical circuits incorrectly joined together.
Worn electrical wire insulation from rubbing against another surface.
Halogen lights making the last few cm of electrical cable insulation brittle/crumble if you disturb it.
HRV incorrectly wired into a lighting circuit.

blindnz

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#2872621 22-Feb-2022 12:51

I get that it would obviously be better to rewire the entire house and in part easier with the wall linings off.

I also understand that to get a proper answer it would require someone to probably look at the cable and check the current load.

On the flipside, I'm sure insulation installers and others don't get a sign-off by the electrician and often do things like blown fill insulation. If they do get sign off every time than that in it's own right would be interesting.

I'm not looking to the internet to let me know the answer/sign-off, but to point me in a direction.

I am asking if someone has had experience with this before or if someone happened to be an electrician/insulation installer, they might explain the considerations.

blindnz

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#2872628 22-Feb-2022 13:00

rphenix:

I believe this is what your interested in reading up on. Agree with timmmay now is a great time to get an Electrician in also consider if you need RCD's on the circuits, or extra power points. I would jump on builderscrack and ask for a quote for a checkup.

Having done a few renovations with friends I've seen quite a few 'shockers'. Ive seen at least one example of:

Redundant live wires.
Electrical circuits incorrectly joined together.
Worn electrical wire insulation from rubbing against another surface.
Halogen lights making the last few cm of electrical cable insulation brittle/crumble if you disturb it.
HRV incorrectly wired into a lighting circuit.

Thanks! Yeah I've seen some of that in other houses when replacing fittings. I've also read the link before but reading it again makes it a bit clearer.

The wiring itself despite being old is a TPS cabling in reasonable condition. Interestingly pink batts make reference to a 1989 date? Maybe this was when some of the wiring mentioned mentioned (TRS) was no longer allowed.

I'll try and get a local electrician to take a look and give me some reassurance.

elpenguino

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#2872633 22-Feb-2022 13:08

blindnz:

The house I'm renovating has older TPS cable which is in good condition. I understand that it can halve the current carrying capacity by 50% if the wiring is surrounded by insulation.

If the capacity of the cable is reduced the protection (circuit breaker or fuse rating) of the circuit would need to be changed (i.e. reduced).

You want to maximise the performance of the insulation so don't tuck or fold.

There's a table in the electrical regulations which shows an electrician how to de-rate the capacity of the cable depending on the environment it is in.

Talk to your electrician for the answers.

Most of the posters in this thread are just like chimpanzees on MDMA, full of feelings of bonhomie, joy, and optimism. Fred99 8/4/21

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blindnz

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#2872719 22-Feb-2022 14:16

elpenguino:

blindnz:

The house I'm renovating has older TPS cable which is in good condition. I understand that it can halve the current carrying capacity by 50% if the wiring is surrounded by insulation.

If the capacity of the cable is reduced the protection (circuit breaker or fuse rating) of the circuit would need to be changed (i.e. reduced).

You want to maximise the performance of the insulation so don't tuck or fold.

There's a table in the electrical regulations which shows an electrician how to de-rate the capacity of the cable depending on the environment it is in.

Talk to your electrician for the answers.

Awesome, that's pretty clear. Depending on the gauge of the wire surrounding the wire reduces the current capacity by ~50%. So for argument sake 2.5mm with a capacity of 24A, would drop to 12A. And therefore if this was currently on a 16A breaker might need to be reduced.

Cool, Will chat to an electrician and get them check the current wiring and the circuits.

gregmcc

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#2872837 22-Feb-2022 17:03

blindnz:

Reaching out to see if anyone has come up against this?

I've recently pulled the Gib and I am retrofitting insulation into the all cavities (internal and external) for heat and noise reasons.

On the side of the pink batts it has a caution for electrical wiring pre 1989 as it may overheat, but makes no reference on what to do in any of the install guides. Rather most of these recommend fitting the insulation close and tight to the wiring. In some online guides people split the batts and run the wire through the batt and in others they tuck behind.

The house I'm renovating has older TPS cable which is in good condition. I understand that it can halve the current carrying capacity by 50% if the wiring is surrounded by insulation.

To get around this I'm not sure if I should run the wiring through conduit, notch the batts or do nothing. Anyone dealt with this before?

I'll try to not get too technical, but if you need clarification ask.

Ok, so standard TPS (90's era) is rated for a temperature of 75 degrees.

When cables are in use they have a very small amount of resistance and this acts as a heater element, the longer distance, the bigger the current load the more heat is generated.

The cable and circuit breaker would have been sized as to not exceed this temperature rating when installed, going above this causes things to burn, such as wood in wall framing or the paper on the gib backing.

When you add insulation this causes more of a heat build up (the calculation tables for temp rise are different to cable with no thermal insulation). So adding insulation to a wall with cables could cause excessive heat build up and potentially a fire.

I think in the 90's the standard rating for TPS was upped to 105 degrees (correct me if i'm wrong).

The reason for splitting the insulation too allow the cable to run thru the middle is because of mechanical damage from screw/nails etc when pictures or what not's are put up.

So where to.....

Talk to your electrician, if you have re-wireable fuses or really old circuit breakers, consider upgrading your fuse board, these provide "coarse" protection, where as modern circuit breakers provide "close" protection.

Arc fault circuit breakers may be another option if you have concerns about the state of your wiring vs. a re-wire

but most of all talk to your electrician as without a close look at things making comments here is only very general advice.

Greg

Registered Electrical Inspector.

SATTV

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#2872966 22-Feb-2022 21:07

If your external walls does not have building paper then you should add that before putting in the insulation.

Just something else to concider.

John

I know enough to be dangerous

k1w1k1d

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#2872988 22-Feb-2022 22:01

I assume you have got a building consent to insulate the walls?

blindnz

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#2873005 22-Feb-2022 23:10

k1w1k1d:
I assume you have got a building consent to insulate the walls?

Last couple of posts are a bit of topic. Yes the external walls will be lined/strapped, as per the NZS for retrofit and will retain the required cavity.
You are correct that external, but not internal insulation requires council consent. However depending on your council, there are still exemptions avenues for low risk work, owner builder or other avenues.

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AACTech

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#2874118 24-Feb-2022 15:29

Just a side note. Any compressiuon of batts reduces the insulation rating as the air spaces air decreased. If you remove the interior lining insulate with modern rigid foam insulation panels - R 4 - resulting in reatly reduced heating and cooling costs no matter where you ive in NZ