Loft / Attic space running cables

[charlie76]

Evening folks. Just out of interest I wondered what methods you guys are using in lofts / attics to keep your cables out of the mountains of insulation you can find these days?

Are you running your cables under insulation against the plasterboard or are you trying to clip to the roof trusses and drop down where required to keep out of it all together?

I ask because i'm currently on a rewire which has had insulation run between the ceiling joists as well as across them. You don't see any timber on the floor of the loft. I'm tempted to clip above and drop where needed.

 

[joehat]

Always see it underneath it and at 6a mcb it's fine


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[Wonderwall]

You've got to wonder about all the 6mm cable feeding showers which have now been covered in mountains of insulation.Some of it has been there for a long long time. Can't say I've had an issue with it to be fair during testing.

 

[Risteard]

You've got to wonder about all the 6mm cable feeding showers which have now been covered in mountains of insulation.Some of it has been there for a long long time. Can't say I've had an issue with it to be fair during testing.

That's because a shower cable won't usually be continuously carrying current for any length of time, and therefore hasn't time to heat up.

 

[charlie76]

You've got to wonder about all the 6mm cable feeding showers which have now been covered in mountains of insulation.Some of it has been there for a long long time. Can't say I've had an issue with it to be fair during testing.

Run the shower for an hour and check Zs.

 

[Wonderwall]

Run the shower for an hour and check Zs.

I don't think the zs would change. The ins resistance might though.

 

[Wonderwall]

That's because a shower cable won't usually be continuously carrying current for any length of time, and therefore hasn't time to heat up.

I wasn't disputing that. I agree.
Do you then think we are wasting our time and money running 10 and 16 mill cables to showers?

 

[charlie76]

I don't think the zs would change. The ins resistance might though.

Why not? Why would the IR change? And if anything the IR would increase which is only a good thing. Zs would increase due to your higher operating temp would cause R1 + R2 to increase and therefore having to dissipate more power.

 

[Darkwood]

If a cable is loaded to less then a certain % of it CCC then insulation can be negated from the calc's, this is usually but not always the case with lighting, when it comes to shower cables then you cannot assume a short duration of use in your calcs but you need to design it for continuous use at the FLC of the shower to ensure the cable will not be subject to any periods of temperature gain that could damage it.
Yes in the real world things don't happen like that but the fact they can means you have to design for the worse case scenerio.

 

[Wonderwall]

Why not? Why would the IR change? And if anything the IR would increase which is only a good thing. Zs would increase due to your higher operating temp would cause R1 + R2 to increase and therefore having to dissipate more power.

how would insulation resistnce increase during higher operating temperatures ?

 

[rich.250]

Evening folks. Just out of interest I wondered what methods you guys are using in lofts / attics to keep your cables out of the mountains of insulation you can find these days?

Are you running your cables under insulation against the plasterboard or are you trying to clip to the roof trusses and drop down where required to keep out of it all together?

I ask because i'm currently on a rewire which has had insulation run between the ceiling joists as well as across them. You don't see any timber on the floor of the loft. I'm tempted to clip above and drop where needed.

We don't try to avoid it,
You could spend lots of trying to avoid it only to pass through it down to a socket and have to derate it anyway!
Just use the correct size cable for the installation method.
As said above lighting is absolutely fine even derated by 50% on a 6amp CB.


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[charlie76]

how would insulation resistnce increase during higher operating temperatures ?

Physics. It would increase as does the resistance of copper as temperature increases however it would be irrelevant in the context of electrical theory as it would be a negligible increase. I was responding to your comment that Zs would not increase but you thought IR would change.

I think Zs would increase and would be far more relevant than the change in IR. In the context of this thread the increase in Zs would be due to the increase in the resistance of the cable due to the temperature increase.

 

[Darkwood]

Physics. It would increase as does the resistance of copper as temperature increases however it would be irrelevant in the context of electrical theory as it would be a negligible increase. I was responding to your comment that Zs would not increase but you thought IR would change.

I think Zs would increase and would be far more relevant than the change in IR. In the context of this thread the increase in Zs would be due to the increase in the resistance of the cable due to the temperature increase.

I see what your trying to say here but you are been too broad with your explanation, physics does't treat conductors and insulators in the same manner when heated up, the insulation on cables will have a rating and up to and including this rating the insulation will maintain its dielectric properties, once you exceed this temperature then the insulation itself will begin to breakdown as its chemical bonds are altered and with that its ability to remain an insulating medium.