Cable reels pat testing

[DPG]

It's not always the same figure. It's 12, 15 or 25m depending on csa of cable.

See table 15.4 of code of practice.

 

[DPG]

Always wondered what the red button was for. ?

To be fair a lot of the red buttons are just overload reset buttons.

 

[Mike Johnson]

To be fair a lot of the red buttons are just overload reset buttons.

I'm pretty sure that's what is on my 50m cable reel, certainly not an RCD, I think its old enough that RCD's where not available back then.

 

[pc1966]

13A fuses have Zs limit of 2.3 ohms (Table 41.2) so assuming your supply Zs is around 1 ohm at the socket then if your cable R1+R2 is 1.3 ohm or less no problem?

 

[DPG]

13A fuses have Zs limit of 2.3 ohms (Table 41.2) so assuming your supply Zs is around 1 ohm at the socket then if your cable R1+R2 is 1.3 ohm or less no problem?

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

 

[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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