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?

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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

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.