Cable reels pat testing

[pc1966]

They do give specific limits on length in the ISITEE code of practice though.

Not as such.

They recommend max lengths of 12/15m for 1.25/1.5mm CSA in section 10.10, and also that longer leads should have RCD protection but that might be part of the installation.

However, 15m of 1.5mm is only 0.36 ohm R1+R2 (from OSG Table I1) so well short of any limit on OCPD disconnection.

 

[DPG]

Not as such.

They recommend max lengths of 12/15m for 1.25/1.5mm CSA in section 10.10, and also that longer leads should have RCD protection but that might be part of the installation.

However, 15m of 1.5mm is only 0.36 ohm R1+R2 (from OSG Table I1) so well short of any limit on OCPD disconnection.

But surely table 15.4 must be followed. And extension are tested as non fixed equipment, ie. separately to the installation.

 

[pc1966]

But surely table 15.4 must be followed. And extension are tested as non fixed equipment, ie. separately to the installation.

Where is 'table 15.4' located?

Yes it is separate from the installation, but my point was more about what would you say is a safe maximum length. I only have a copy of the 5th edition ISITEE (ex-PAT) book and, while it has some recommendation on length, no hard limits.

We have all seen extension leads of 50m in use! So the point really is when testing such a lead, what is pass/fail? The ISITEE has flexible cable resistance value in Appendix 5 for the CPC so if you measure a lead and its end-end resistance is in keeping with the cable spec and overall length then it would look like a pass to me (i.e. "working as designed").

However, what is a reasonable limit on an extension lead length?

50m of 1.5mm has R1+R2 of 1.33 ohm (cold, from ISITEE table) and a 13A fuse as max Zs of 2.3 ohms, and with a typical socket outlet being of the order of 1 ohm Zs then that looks like the maximum length that is reasonable for such a lead before you are depending on RCD protection to disconnect.

 

[DPG]

I must admit I haven't got the 5th edition yet, I've only got the 4th. But I was thinking from the point of view of someone doing PAT testing - they will most likely have a big pile of things to test, and each one will be tested individually. They may not have any knowledge of the fixed wiring installation, or even any access to test it.

I take your points though.

 

[pc1966]

My point goes back to the OP's belief the ISITEE has a definite limit and it is less then the 25m cables they had.

Also it would be rare today not to have RCD protection, either at the DB, at an RCD socket outlet (say on older properties for outside use), or if in any doubt a RCD plug-in adaptor.

 

[pc1966]

I am sure some PAT testers have a length-factor you can enter, or at least a table of reasonable values to check against.

 

[westward10]

Again I dont have a new copy of the CoP but I am certain those suggested lengths all equate to 0.18 ohm. I was actually doing some PAT last week on a site where the new workshop had rcd protected sockets but the old did not. They both had these long extension reels and we just recommend they only be used with rcd protection where the earth bond exceeded 0.18 ohm which invariably they do.

 

[pc1966]

We have a rule of thumb that where the earth bond exceeds 0.18 ohm (I believe this equates to the suggested lengths in the CoP) that it is recommended it is only used with 30ma rcd protection

It is a little shorter, works out at 13.5m of 1.5mm flex, not allowing for plug/socket resistance (which ought to be very small).

5% VD at 13A would be 33m of 1.5mm flex, but I suspect it is rare that you would be using a lead at max current and in a situation where strictly meeting that matters.

TL;DR A 50m lead 0f 1.5mm is reasonable max for occasional/intermittent use, if it measures right, in my opinion.

 

[pc1966]

It is a little shorter, works out at 13.5m of 1.5mm flex, not allowing for plug/socket resistance (which ought to be very

Actually if using the resistance from OSG it is about 15m

• OSG table I1 has 12.1 mOhm/m for 1.5mm
• ISITEE table A5.1 has 13.3 mOhm/m for 1.5mm flex

Go figure!

 

[westward10]

Just found this Table and it shows both for different Classes so it is 13.3.

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[pc1966]

Interesting, as that is about 10% difference for what ought to be the same area of copper!

 

[DPG]

I think the text in the 4th edition could be clearer, mainly for when 'PAT testers' rather than electricians are doing the testing. We obviously have more knowledge than people who would often be doing the testing.

Be interesting to see how it is shown in the 5th edition when I get hold of it.

 

[pc1966]

I think the text in the 4th edition could be clearer, mainly for when 'PAT testers' rather than electricians are doing the testing. We obviously have more knowledge than people who would often be doing the testing.

It is an issue for pass/fail equipment intended for relatively unskilled use, and even for the devices that give you an earth bond reading it is not always made clear how to decide if it is a fail (for short cable, as high R must be dodgy connection) or a pass (for extension lead of a given length).

Or indeed what sort of a length actually is reasonable!

Be interesting to see how it is shown in the 5th edition when I get hold of it.

Be prepared for disappointment!

 

[westward10]

Interesting, as that is about 10% difference for what ought to be the same area of copper!

Must admit I expected them to be the same but explains the difference.

 

[brianmoooore]

If you limit the length of extension cables, all you're going to get is multiple extension leads daisy chained together.

 

[DPG]

If you limit the length of extension cables, all you're going to get is multiple extension leads daisy chained together.

Very true. But someone who is PAT/ISITEE testing should be using the code of practice. What someone decides to do with the equipment after that is not their concern.

 

[brianmoooore]

The object of the exercise should be safety. A 100m extension lead is far safer than four 25m ones, which will have three plug and socket joints lying around in random places, getting wet, getting crushed or forming trip hazards.

 

[DPG]

The object of the exercise should be safety. A 100m extension lead is far safer than four 25m ones, which will have three plug and socket joints lying around in random places, getting wet, getting crushed or forming trip hazards.

I agree with that. But if you picture the poor guy you often see with a huge pile of cables and equipment in front of him, all he can do is test things as one-off items. He may well have no visibility of where they will be used.

 

[pc1966]

Very true. But someone who is PAT/ISITEE testing should be using the code of practice.

But is it up to PAT/ISITEE testing to determine if a commercial product, like a 100m lead, is safe or not by design?

Of course they should check it is physically in good condition, and that the cable resistance matches expectations, and the manufacturer's recommended fuse size is fitted.

 

[brianmoooore]

I'm not blaming the guy doing the testing, I'm blaming the ivory tower enclosed muppets that draw up ill thought out legislation.
If a worker needs power 100m away from the nearest power outlet, then he's going to do whatever it takes to get the power there. Those drawing up the legislation should be aware of this and legislate accordingly.