Minimum IR

[mat155]

Good evening. What is the minimum IR for 70mm unarmoured cable?

 

[uksparks]

1M ohm?? If under 2Mohm it needs looking at.

however I don't understand the point of what you are asking?

 

[Andy78]

Good evening. What is the minimum IR for 70mm unarmoured cable?

The minimum IR value does not depend on the size or construction type of the cable, but the voltage it operates at.

 

[mat155]

230v. Is it 1 mohm. Same as domestic? 70mm over 300.

 

[Simonslimline]

Have a look in BS7671.

 

[mat155]

Just out on site it's very cold, wet haven't got regs with me. Just looking for some help. That's all.

 

[Deleted member 9648]

1megohm mate.

 

[Pete999]

Good evening. What is the minimum IR for 70mm unarmoured cable?

What voltage are you operating at????

 

[HappyHippyDad]

Just out on site it's very cold, wet haven't got regs with me. Just looking for some help. That's all.

Feel a bit sorry for him now :sad3: Good on you Wirepuller!

 

[Deleted member 9648]

What voltage are you operating at????

He stated 230v

 

[Pete999]

He stated 230v

Right missed that then

 

[Englishman]

Wherever he is, he shouldn't need to look in regs to find the minimum IR values. It's not exactly difficult to remember is it?

 

[Lucien Nunes]

The OP asks about a particular cable, I wonder if this is significant? The IR for the cable itself will be as per the manufacturer's info and will be inversely propotional to length, given in the form x megohm.km i.e. divide the figure by the length in km to get minimum value in megohms. But for a circuit, including the fittings at both ends and an unspecified length of the cable, as stated above.

 

[Englishman]

He asked what the minimum was, nothing else.

 

[HappyHippyDad]

Well this was 2 hours ago. I hope he's in a warm pub by now worrying about what his highest resistance to alcohol is!

 

[PEG]

The OP has not stated whether or not this is in an industrial setting,or how old the cable is. Some types of cable,in this instance,would have a calculated IR value far below what is stated in any "modern" regs book...and if a previously redundant cable was being brought back into service,monitoring would ensue,to check for a probable rise in IR value.

...1Meg...i hang awake at night,dreaming of 1Meg...:wacko:

 

[mat155]

Good evening gents.

Thanks for the helpful advice where given. Warm and dry now. Sorry for the lack of info. It was motorway spec cable. 150Ohms/L is the minimum. Was not thinking straight due to the frost bite setting in but knew it was there abouts.

Think sometimes to often when a question is asked on here the answer is look at the regs. Sometimes you need a little help in a shtt situation.

Cheers

 

[davesparks]

1 meg is a wonderful 'one size fits all' solution which makes no allowance for any real world factors which may apply to older cables or equipment.
It seems a bit ridiculous to me that a brand new installation only needs to meet this 1meg requirement the same as any old installation is judged by the same standard.
There is an old formula which can be used to relate the minimum value to the individual situation. The insulation resistance should be sufficient to ensure that the earth leakage current is no more than 1/10000th of flc

 

[Deleted member 9648]

The original question asked what the minimum IR value for a 230v cable is as a regs book wasn't to hand, that implies the OP required the minimum value stated in bs 7671...which is 1 megohm!

 

[HandySparks]

It was motorway spec cable. 150Ohms/L is the minimum.

I'm confused. What exactly does this '150Ohms/L' mean?

 

[PEG]

Good evening gents.

Thanks for the helpful advice where given. Warm and dry now. Sorry for the lack of info. It was motorway spec cable. 150Ohms/L is the minimum. Was not thinking straight due to the frost bite setting in but knew it was there abouts.

Think sometimes to often when a question is asked on here the answer is look at the regs. Sometimes you need a little help in a shtt situation.

Cheers

Hi bud,this would have been easier,if we knew the situation and type of cable.

Where has the "1500hms/L" come from? :smiley2: ...or "150 Ohms/L" even?

 

[Lucien Nunes]

The original question asked what the minimum IR value for a 230v cable is as a regs book wasn't to hand, that implies the OP required the minimum value stated in bs 7671...which is 1 megohm!

It's no longer clear exactly what the OP was asking but there's an important difference between the minimum acceptable IR for 70mm² cable and the IR for a circuit using that cable. 1 metre of 70mm² would be considered faulty and rejected if it could only achieve 1MΩ, but wire it between a fuse-switch and a busbar chamber and test it on a damp day and 1MΩ might be realistic. OTOH a 600m run of cable might not be so bad at 1MΩ so when you are looking at larger cables and longer runs you can't just say 1MΩ is the limit and that's that.

Hence the figure in MΩ.km (sometimes misquoted as MΩ/km which is a nonsense) that manufacturers give for each size and type of cable, or they refer to the one in the BS for that cable. If the '150 ohms/l' is supposed to say megohms then it makes sense to me.

 

[LeeH]

I'm confused. What exactly does this '150Ohms/L' mean?

Lorry
Litre
Lepricon?

 

[mat155]

Spanner in the works. 1500 Ohms or 1.5MOhms is the minimum per kilometer / by the Length is the minimum for motorway spec power cable. Typo after one of those days where you are glad to put behind you. Thanks all the same.