cables under insulation in loft

[Andrew M]

Hi Andy,

yeah,I can't though that's the thing.

The shower cable run is about 12/14 feet and the most I can lift the cable at any point is about 6 inches so not much hope of getting 170mm of fibre under there and if I did it would be very tight.

Are there any other options I can consider?

Cheers for your reply.

 

[SPECIAL LOCATION]

I've had the lights on for a few hours now and there does not appear to be a problem so far also I just used the shower and again there doesn't appear to be anything out of order, I was in there for quite a while too as I was stinking from being in the loft all day.

I would appreciate what you chaps think of all this and I'm a big boy so say it as it is because I need a few opinions before I can sign this job off in my head,as it is now I'm halfway to going back up there now and uncovering the shower cable but in the same breath I think I'll let it sit for a few uses first as well.

Sorry but I have no idea about what kind of cables have been used up there but the shower cable looks like a real beast compared to the lighting runs.

Many thanks in advance.

Without any actual figures of the loading of the circuits or the cable sizes it is impossible to say that there will or wont be a problem....

On the one hand if the cables are big enough already then you may have wasted your time doing what you have done....

on the other hand maybe not.......

just switching something for a while "to see if there is a problem" proves nothing...

If you do have genuine concerns or worries then I would suggest get an electrician to come round and have a look....

As I presume from the wording of your question that you are not electrically qualified and this is a DIY project?

Need more facts and figures to give any definitive answers IMHO.

:coffee

 

[Andrew M]

Hello Trailer Boy and thanks for replying,

I'll start at the bottom of your reply and work up.

No,I am not electrically qualified and this is a DIY  project yes.

It's such a tight squeeze to get access to this loft that I seriously doubt anyone else apart from me would want to or be able to get up there.

I understand that having things working now does not mean that they will continue to work if there is a chance of a problem later down the line.

When you say,

''On the one hand if the cables are big enough already then you may have wasted your time doing what you have done...
on the other hand maybe not.......''

do you mean that if the cables are rated sufficiently high enough then burying them under the insulation would not have been a problem regardless of using the guttering as ducting?


I probably will not be able to get back up there until next weekend now but if I could provide you with a physical measurement in millimetres of any cable up there would that be enough for you to be able to tell the rating of those cables?

Again many thanks for your reply.

 

[Andrew M]

What do you all think of that idea to use the guttering to give the cables a little room to breath and stay cool,was it worth the effort overall?

I don't think doing that could have hurt at all?
Or did adding more plastic up there not help at all?


If there was to be a problem with the shower cable now,how could I expect that to manifest itself?
If the cable overheats too much surely the trip switch will go before the cable itself melts and becomes a fire hazard?

 

[Technician]

If the cable overheats too much surely the trip switch will go before the cable itself melts and becomes a fire hazard?

What trip switch?

 

[Andrew M]

The trip switch in the fuse box.

 

[Technician]

The trip switch in the fuse box.

If the cable overheats to such a degree that it might be a fire hazard

before anything like this happens then clearly there is something wrong.

 

[Andy™]

If the cable overheats too much surely the trip switch will go before the cable itself melts and becomes a fire hazard?

the MCB ( / fuse) is designed to detect overload and fault currents. it will not stop a cable overheating because you have put insulation ontop of it. the MCB will only trip once it has melted enough to cause a large enough fault current. the MCB & cable must be matched to suit the installation. if you add insulation, then they may not now work since you have changed the design of the cable

although it does sound more like your a DIYer wanting to insulate the loft a bit more but taking time to check the wiring is safe rather than just throwing as much insulation around the cables as possible

 

[Andrew M]

If the cable overheats to such a degree that it might be a fire hazard

before anything like this happens then clearly there is something wrong.

How likely is this to happen though?

 

[Andrew M]

Thanks,

I did read up a bit before I went up there and from what I could gather the general consensus was that a lighting circuit would be ok under a bit of insulation but it was the power/shower cables that you had to watch because of them running closer to their capacity.

I had the idea to place the guttering over all the cables as I thought that would allow an air flow around the cables keeping them cooler than they otherwise may be although clearly it is impossible to measure if there is any reality to that thinking.

I think now I may have to go back up there tonight and find a way to bring the shower cable up to the fresh air which will probably mean having to remove a good deal of the insulation but if that means I can sleep at night it's no worry.

I know the trip switch module in the fuse box is 45amp rated as I replaced that unit in the last 12 months as it failed and I think the shower cable used up there is pretty heavy duty stuff as it is one of the bigger electric cables I've seen,quite a lot thicker than the power cable that runs to the plugs for the tv and pc etc that I can see in the eaves that I can access on the lower level of the place.

As I say this place was updated about 10 years ago and had a full rewire then so I suppose I was hoping that the cables would be able to take a bit of abuse but,of course,having now done the job I can't help but wonder if I've created more problems than I solved and at the end of the day removing the shower cable from under the insulation appears to be the only answer to that.

Thank you very much for your input chaps and please add if you think there's anything more to be said.

 

[Technician]

How likely is this to happen though?

Size the cable incorrectly without taking account of the appropriate

re-rating factors and damage will almost certainly follow and that is

enough even if a fire hazard is not created.

 

[Andrew M]

Size the cable incorrectly without taking account of the appropriate

re-rating factors and damage will almost certainly follow and that is

enough even if a fire hazard is not created.

True and I can't piss about with that to be fair,I'm sure the cable is heavy duty stuff but that's not enough to put my mind to rest over the long term so it looks like another trip to dark and dusty hellhole for me soon.

 

[Andy™]

How likely is this to happen though?

well if the cable is running right at its limit to start with, and you fully enclose it in insulation, then it could take minutes to melt

a cable design correctly and running at its limit will get to 70 degree's. now if it cant get rid of that heat fast enough...

 

[Nicky Tesla]

Ring circuit cables are to derate to a minimum of 20A for the normal 32A socket cct.   150mm insulation derates 2.5t&e to about 17.5 as ai recall (correct me if im wrong).  But the question is, is under what criteria is cable rated?    At 20a rating,  does this mean that the cable needs to be drawing 20a for a whole hour or so without any damage?   Im sure it is something like this.   As we know,  circuit currents are rather sporadic and the chance of drawing 20A for over an hour is improbable.   A shower cable will usually draw a large current for say 10min at a time.  Due to this aspect i personally dont think the extra insulation causes a problem.

Anyone used basket like snake tray in a loft?  i think it would make sense sometimes.

 

[Andrew M]

Cheers,

when you say circuit currents are sporadic would that explain why lights flicker and the temperature of the water coming from an electric shower can vary?

 

 

[Technician]

    At 20a rating,  does this mean that the cable needs to be drawing 20a for a whole hour or so without any damage?  

There is a clear statement in Guidance note 6 which identifies the need

to ensure that Ib (design current/load) is sufficiently high to include all of the

forseeable peak loads of a protracted nature.  This is why we have the

informative appendix 15 in the regs.

A further statement also identifies that estimation of cable life can only be an

approximation.

 

[Nicky Tesla]

Cheers,

when you say circuit currents are sporadic would that explain why lights flicker and the temperature of the water coming from an electric shower can vary?

No thats voltage.  What i mean is,  there have been studies of ring circuit currents showing many ups and downs when say a washing machine is heating  or a kettle is boiling etc.   Therefore current is never at a stable level  where design current for a motor or pump that was spinning for hours on end would be stable which means the heating effect on the cable itself will be more predictable and the design current will  be the actual current.  

 For eg if a circuit was designed to draw a steady 1A for hours and occasionally draw 20A for 1minute, logicaly i dont think there is a need to use cable rated to 20A as there is not enough energy created in 1min to effect the cable.

 

[Andrew M]

Thank you,you are opening my mind the the hows and whys of electrical operation,rating and safety.

 

[Andrew M]

not me for sure

 

[Sidewinder]

How many do you know who 

a. Own GN6

b. Have read GN6

c. Can understand GN6

And chucked in for the rest of the GN's - How many know what GN 1-8 is ? :slap

Not true - That would depend on the nature of the load on the motor 

I can give many real life examples if required including a 30kW pump i was working on over Christmas (on a breakdown)

Do I count?..

Was going through GN8 earlier to look into an issue!