parallel conductors and neutral switching of through contactors in lighting circuits

[Cazmac1]

Hi guys, I have come across two problems today well acutely three so I will list them first..

1st
Testing a 4mm radial circuit today or so I thought! I asked the young lad to go to the end of line and take an r1+r2 reading. When he opened up the last point he said that there were four 2.5 cables in the socket two netrals and two lives, I first thought I had made a mistake and check to make sure that the circuit was indeed a rad and not a ring. No problem there. I then thought he must have the wrong circuit but a quick live test proved it was the correct circuit.
I then started to look at the causes, It turns out the the 4mm was feeding a 20amp double pole sw and from there they had used 2.5mm conductors so I presume they had run out of 4 mm so double up on 2.5! I have seen this done on site temps but never on a new install. now you can see the confusion it caused me so it is clearly bad practice. But my question is it against the regs???

2nd

Found really badly wired contactors, I won't bore you with all the details but there were four contactors all being controlled by a time clock (nothing wrong there) there was only 3 lights on two circuits and 4 on the other two( Nothing wrong there) Just trying to give you a feel for the circuits and what they are controlling.
Like I said I don't want to go into all the wiring problems but I do have a question, the neutrals on the lights were wired through the contactor, so the contactor is effectively acting as a double pole switch. Can someone tell me is this standard practice to wired the neutral through the contactor. I have been told that were automatic disconnection of supply takes place both conductors must be switched. This seem unnecessary to me as the contactor is merely acting as switch. The contactors are really old and while testing I was getting a great smell of burning I have yet to work out if this is from the coil or the load current through the contacts( testing on going circuit out of use) I just think if the neutral contact burns out then I will have a neutral conductor O/C and sitting at mains voltage. What is common practice and what does the regs say? will look when I have time but if some one has the answer all the better.


3rd
keep this short and sweet

testing a three phase sub main to a remote DB. when looking for the DB (poor description of location) could not find DB with new phase colour cable. physically traced cable up in to the loft where we found the cable had been jointed trough an adaptable metal box and then though crimped and insulated with electrical tape! to an existing cable's with old colours. Yet again lack of information and bad practice led to confusion and could lead to a highly dangerous situation. Thoughts on this one please.


Look forward to your replies tomorrow.

 

[davesparks]

Re: parallel conductors and neutral switching of through contactors in lighting circu

Item 2
You can either use a contactor to switch the live or the live and neutral but never just the neutral.
If I am switching one circuit through a 2 pole contactor I will switch both as it saves adding another terminal block in to the enclosure.

Item 3

Nothing wrong with having a joint in a submain as long as it is correctly made. A joint between old and new colours should be suitably marked up according to the regulations.

As to whether insulation tape is suitable to insulate a connector, a lot of people will get very excitable about that.
It's certainly not the ideal method but if it is in good condition and the tape isn't falling off then there's not much you can say against it.

 

[Cyril Molony]

Re: parallel conductors and neutral switching of through contactors in lighting circu

Item No.1 though not standard but comply with regulations as 2 x 2.5 mm greater CSA then 4 mm feed to 20A DP switch, I am assuming 20 A Circuit breaker, it would not have complied if feed was 6 mm, then it would fail 433.2.1 Page 82 BS7671 : 2008 (2012). As long as you mark up board schedule and state on test sheet then present configuration ok. if 32A circuit breaker then 4 mm or 2 x 2.5 mm may not comply (see Table 4D5 page 340).

 

[Cazmac1]

Re: parallel conductors and neutral switching of through contactors in lighting circu

Item No.1 though not standard but comply with regulations as 2 x 2.5 mm greater CSA then 4 mm feed to 20A DP switch, I am assuming 20 A Circuit breaker, it would not have complied if feed was 6 mm, then it would fail 433.2.1 Page 82 BS7671 : 2008 (2012). As long as you mark up board schedule and state on test sheet then present configuration ok. if 32A circuit breaker then 4 mm or 2 x 2.5 mm may not comply (see Table 4D5 page 340).

Yes your correct 20 a CB.

 

[Cazmac1]

Re: parallel conductors and neutral switching of through contactors in lighting circu

With the contactors apart from the control circuit S1 - S2 I would have put all the neutrals in the neutral buzz bar of the DB. less cables in the contact enclosure and less room for error.

If I was jointing a three phase cable I would have used a torpedo, as to using insulation tape I never use it as a permanent insulator as it can break down over time. In this case I would have used heat shrink.

If the joint is allowed I will as with the parallel conductors I will just update the shedule to reflect this.

 

[Engineer54]

Re: parallel conductors and neutral switching of through contactors in lighting circu

Item No.1 though not standard but comply with regulations as 2 x 2.5 mm greater CSA then 4 mm feed to 20A DP switch, I am assuming 20 A Circuit breaker, it would not have complied if feed was 6 mm, then it would fail 433.2.1 Page 82 BS7671 : 2008 (2012). As long as you mark up board schedule and state on test sheet then present configuration ok. if 32A circuit breaker then 4 mm or 2 x 2.5 mm may not comply (see Table 4D5 page 340).

So what about a 6mm cable on a 32A MCB/RCBO supplying a 2.5mm ring circuit (lollipop ring circuit)?? are you saying this circuit wouldn't comply?? FYI, non standard circuits do comply provided they meet or exceed general circuit criteria laid out in BS 7671!!

 

[Pete999]

Re: parallel conductors and neutral switching of through contactors in lighting circu

Item No.1 though not standard but comply with regulations as 2 x 2.5 mm greater CSA then 4 mm feed to 20A DP switch, I am assuming 20 A Circuit breaker, it would not have complied if feed was 6 mm, then it would fail 433.2.1 Page 82 BS7671 : 2008 (2012). As long as you mark up board schedule and state on test sheet then present configuration ok. if 32A circuit breaker then 4 mm or 2 x 2.5 mm may not comply (see Table 4D5 page 340).

Why wont it comply have you looked at app 15 4mm radial 32amp ocpd?

 

[Engineer54]

Re: parallel conductors and neutral switching of through contactors in lighting circu

Why wont it comply have you looked at app 15 4mm radial 32amp ocpd?

I was just wondering if Cyril works for NICEIC?? lol!!

 

[sparkymalarky]

Re: parallel conductors and neutral switching of through contactors in lighting circu

I was just wondering if Cyril works for NICEIC?? lol!!

I like this. I like this a lot! lol.

 

[Lucien Nunes]

Re: parallel conductors and neutral switching of through contactors in lighting circu

Precautions need to be taken with parallel cables to avoid one losing continuity without affecting the other, as the circuit would carry on working with undersize cable. I'm not sure that I trust four 2.5's in a socket terminal to meet that requirement, sorry can't remember the reg number. OTOH if it's a 20A circuit I wonder what the requirement for the parallel cables is. VD? Zs?

 

[snowhead]

Re: parallel conductors and neutral switching of through contactors in lighting circu

I'm not sure that I trust four 2.5's in a socket terminal to meet that requirement,

2 Live
2 Neutral

It's not 4 in a terminal.

 

[Lucien Nunes]

Re: parallel conductors and neutral switching of through contactors in lighting circu

But that's the last point. Presumably the ones before will have four cables.

 

[davesparks]

Re: parallel conductors and neutral switching of through contactors in lighting circu

Or there will at least be one with the 4mm and 2x 2.5mm

 

[Cyril Molony]

Re: parallel conductors and neutral switching of through contactors in lighting circu

Why wont it comply have you looked at app 15 4mm radial 32amp ocpd?

If you look at page 340 Table 4D5 - 70 degree Celcuis thermoplastic insulated and sheathed flat cable with protective conductor

4mm Method 100 Itab = 27A, 4mm method 101 Itab = 22A, Method 102 4mm = 27A, only Method C clipped direct complies where I =37, if conductor where singles enclosed in conduit method B Table 4D1A 4mm Itab =32A then 4 mm would comply.

When considering the original question I looked up Table 4D5 So I stand by my original statement 4 mm may not comply for current carrying capacity, it will depend on installation method.

 

[Cyril Molony]

Re: parallel conductors and neutral switching of through contactors in lighting circu

So what about a 6mm cable on a 32A MCB/RCBO supplying a 2.5mm ring circuit (lollipop ring circuit)?? are you saying this circuit wouldn't comply?? FYI, non standard circuits do comply provided they meet or exceed general circuit criteria laid out in BS 7671!!

Dear engineer you need to read the reg I quoted again apart from some exemption when you reduce conductor sizes eg from 6 mm to 5 mm (2 x 2.5 mm) you should fit protective device, in the original question a 20A DP switch was used, so would 6 mm comply, if you fitted some form of protective device. I have no problem with non standard circuits, that the general point I was expressing

 

[Cyril Molony]

Re: parallel conductors and neutral switching of through contactors in lighting circu

I was just wondering if Cyril works for NICEIC?? lol!!

No not NICEIC I am a retired JIB electrician.

 

[Engineer54]

Re: parallel conductors and neutral switching of through contactors in lighting circu

Dear engineer you need to read the reg I quoted again apart from some exemption when you reduce conductor sizes eg from 6 mm to 5 mm (2 x 2.5 mm) you should fit protective device, in the original question a 20A DP switch was used, so would 6 mm comply, if you fitted some form of protective device. I have no problem with non standard circuits, that the general point I was expressing

My question to you, was will a 6mm/2.5mm lollipop ring conform sitting on a 32A MCB/RCBO protective device??....

Providing all other critera conforms, then the 32A protective device will be good to to protect both the 6mm radial section and the ring 2.5mm section, so will therefore comply... The lollipop ring has been used and generally accepted as a non-standard circuit for as far back as i care remember. There is no need to fit a protective device at the point of cable size reduction.

 

[HandySparks]

Re: parallel conductors and neutral switching of through contactors in lighting circu

My question to you, was will a 6mm/2.5mm lollipop ring conform sitting on a 32A MCB/RCBO protective device??....

Providing all other critera conforms, then the 32A protective device will be good to to protect both the 6mm radial section and the ring 2.5mm section, so will therefore comply... The lollipop ring has been used and generally accepted as a non-standard circuit for as far back as i care remember. There is no need to fit a protective device at the point of cable size reduction.

Totally agree with you here E54 (there's a first!).

BS 7671 2008 Amdt 1, para 433.2.1 requires a device for protection against overload to be installed at the point where a reduction occurs in the value of current-carrying capacity of the conductors of the installation.

I was going to say that this reg appears to be nonsensical and should be ignored. Then I spotted 433.3.1 (i):

"A device for protection against overload need not be provided for a conductor situated on the load side of a point where a reduction occurs in the value of current-carrying capacity, where the conductor is effectively protected against overload by a protective device installed on the supply side of that point."

Following on from the lollipop example, if I chose to use 2.5mm² for the first leg of a 6A lighting circuit to reduce voltage drop, and then 1mm² for the final legs to ease termination to accessories, the 6A breaker at the origin would be entirely adequate to protect the whole run.

If 433.3.1 didn't exist, you'd have to fit an overload protective device wherever a cable ran through an insulated wall!

 

[Engineer54]

Re: parallel conductors and neutral switching of through contactors in lighting circu

There's always a first for everything HandySparks!! lol!!

With regards to the subject in hand, your example is yet another good example where a reduction in cable size does not automatically call for a protective device to be installed.

Not interested that much in 433.3.1 i don't take BS7671 as the Be All and End All of electrical installations, i treat it as an informed guide only, but then most of my alternatives will tend to be over and above anything that BS7671 and it's GN's will call for!!