Cable reels pat testing

[McTadder]

Found two 25m cable reel extensions on a pat test yesterday with no RCDs should they be automatically taken out of service. They were at least 10 years old. The 5th addition says up to 15m max?

 

[westward10]

You can get extension reels in all sorts of length I see Screwfix selling a 45m one, from a reputable supplier. 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, of course this does not take into consideration any volt drop issues.

 

[McTadder]

You can get extension reels in all sorts of length I see Screwfix selling a 45m one, from a reputable supplier. 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, of course this does not take into consideration any volt drop issues.

Unwound the 25m reel was failing at 0.56 ohms. Before I started doing the maths to check !

 

[westward10]

Your tester probably has a default setting and sees the earth bond reading as too high when in fact it is just the nature of reels length.

 

[Moley]

What tester are you using? Some have settings for different length reels or a setting to put your own pass/fail value in if it's an odd length reel.

 

[McTadder]

What tester are you using? Some have settings for different length reels or a setting to put your own pass/fail value in if it's an odd length reel.

Seaward Apollo 500 + I thought there was a built in calculator but couldn’t work it out on site. Have to read the manual again?

 

[Mike Johnson]

Not very manly reading the manual, obviously in touch with your female side. ?

 

[i=p/u]

Just says it should be used with rcd, so make sure plugged into rcd protected socket or buy plug in unit..

 

[DPG]

You can't take them out of service for not having RCDs. The socket feeding them will more often than not have RCD protection.

 

[McTadder]

You can't take them out of service for not having RCDs. The socket feeding them will more often than not have RCD protection.

Are you talking about the RCD on the DB ??? They’re certainly not using a plug in RCD.

 

[i=p/u]

Either or is recommended.

 

[DPG]

Are you talking about the RCD on the DB ??? They’re certainly not using a plug in RCD.

But it's an extension lead, not a permanent bit of wiring. Can be plugged into any 13A socket.

 

[DPG]

Sorry, I've just realised the length of cable is your issue. I ignored that bit in my rush to read it. I'll dig out my code of practice and remind myself what it says.

I'm pretty sure you're right though. Isn't it over 12m they need to have a built in RCD?

Haven't got the 5th edition yet, not sure if anything has changed in that. I suspect not.

 

[i=p/u]

Says 15m and anything longer should have rcd incorporated, along them lines...

 

[Mike Johnson]

Always wondered what the red button was for. ?

 

[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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