Class 2 consumer units

[steptoe]

So you can consider using a metal one then conclude that's a bit stupid??

Brilliant,  :Applaud

I've often thought, as deviations are allowed from BS7671, that I can fit a plastic CU and note under deviations,

' a plastic CU has been fitted as it was fitted by a competent person and not a 5WW with limited knowledge'

 

[Rob_the_rich]

So you can consider using a metal one then conclude that's a bit stupid??

This would be a good situation to use a plastic CU and encase it in a metal enclosure.

The reason the osg (and IET's policy committee) give is that the tails could come loose and touch the metal casing. In TT the EFLI could be high enough such that the OCPD (cut-out) does not disconnect the supply within 5 secs. It then suggests 3 bits of advice

a) class II metal CU

b) class I metal CU with all RCBOs

c)split load class I metal CU with DP 100mA TD RCCB main sw.

Neither b) nor c) actually solve the problem of a loose tail, which is a bit poor IMO.

Best solution I think is an external 100mA s-type RCCB DP sw in a plastic enclosure (eg rec2), then a class I metal CU.

 

[Essex1]

Brilliant,  :Applaud

I've often thought, as deviations are allowed from BS7671, that I can fit a plastic CU and note under deviations,

' a plastic CU has been fitted as it was fitted by a competent person and not a 5WW with limited knowledge'

You can deviate from BS7671 as long as you meet the same level of protection that BS7671 affords. 

 

[Andy™]

Best solution I think is an external 100mA s-type RCCB DP sw in a plastic enclosure (eg rec2), then a class I metal CU.

but the box for the RCD has the same requirements as the CU

 

[Rob_the_rich]

but the box for the RCD has the same requirements as the CU

it doesn't, it is not an "assembly", no need for metal. In fact all insulated is preferred because of the loose tail scenario

 

[Essex1]

I think a separate RCD and enclosure would need to be NC.  

 

[Manator]

it doesn't, it is not an "assembly", no need for metal. In fact all insulated is preferred because of the loose tail scenario

@Rob_the_rich  I am afraid it does, the amendment does not restrict itself to consumer units.

 

[Sidewinder]

Once the IET guide is out (due March I think), I'll post the gist of it as it's part of my subscription.

 

[steptoe]

Has anyone took a blowtorch to a normal plastic CU,?

I'd put money on that when you remove the flame it stops burning,

I'd also bet, if you take a welding/cutting torch to a metal CU it will also burn until you remove the flame,

So, what have we learned from this,? 

 

[Andy™]

i got a old plastic CU... wonder how well it will go against acetylene?

 

[SPECIAL LOCATION]

This would be a good situation to use a plastic CU and encase it in a metal enclosure.

The reason the osg (and IET's policy committee) give is that the tails could come loose and touch the metal casing. In TT the EFLI could be high enough such that the OCPD (cut-out) does not disconnect the supply within 5 secs. It then suggests 3 bits of advice

a) class II metal CU

b) class I metal CU with all RCBOs

c)split load class I metal CU with DP 100mA TD RCCB main sw.

Neither b) nor c) actually solve the problem of a loose tail, which is a bit poor IMO.

Best solution I think is an external 100mA s-type RCCB DP sw in a plastic enclosure (eg rec2), then a class I metal CU.

Some of the context of the notes re the tails is not just the supply tails....

See the note starting bottom of Pg 20.

It talks about a split load metal enclosure with single insulated tails between main switch & RCD's as having a much greater risk of live contact with enclosure...

compared to a fully RCBO'd metal board.

which to some degree I can see their point on that aspect...

i.e. metal enclosure split load TT board is not recommended.

whereas a fully RCBO'd metal TT board is much better.

opcorn

 

[Essex1]

Has anyone took a blowtorch to a normal plastic CU,?

I'd put money on that when you remove the flame it stops burning,

I'd also bet, if you take a welding/cutting torch to a metal CU it will also burn until you remove the flame,

So, what have we learned from this,? 

Yes. The LFB did and the results were alarming. 

 

[Rob_the_rich]

@Rob_the_rich  I am afraid it does, the amendment does not restrict itself to consumer units.

"consumer units and other switchgear assemblies"

Assemblies are made up of switchgear and controlgear,

An RCCB is just one unit.

The beama guide http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjr15K1jNXKAhVGYg8KHc0WAKwQFggfMAA&url=http%3A%2F%2Fwww.beama.org.uk%2Fasset%2F7DF1EEE0-F314-452B-81E276BC561F4B89%2F&usg=AFQjCNE72N3VpAbRL3dcAKq9ivQ6Ev5oyA does not mention an RCD in an enclosure. The similar switchgear assemblies it says are in scope all have separate units for switching and for control, those not in scope include various RCDs. I fail to see how an RCD in an enclosure needs a metal box.

 

[SPECIAL LOCATION]

Has anyone took a blowtorch to a normal plastic CU,?

I'd put money on that when you remove the flame it stops burning,

I'd also bet, if you take a welding/cutting torch to a metal CU it will also burn until you remove the flame,

So, what have we learned from this,? 

you're a secret pyromaniac wanting to ignite everything.?

:innocent Guinness

 

[Sidewinder]

@Rob_the_rich, I agree with you, but, the scams & the IET don't.

I'll try to dig out the info as soon as I get a chance, but, that may be days or weeks, sorry.

 

[NozSpark]

Has anyone took a blowtorch to a normal plastic CU,?

I'd put money on that when you remove the flame it stops burning,

I'd also bet, if you take a welding/cutting torch to a metal CU it will also burn until you remove the flame,

So, what have we learned from this,? 

I've seen a PVC mobile home hook up box that was on fire due to a faulty RCD

About 20 seconds after the power was turned off the flame went out..

After that I wired all the hookups SUB MAIN - MCB - RCD

 

[binky]

The what ? Thats new to me !

how too calculate the actual size of the main earth cable needed instead of just bunging 16mm in every house cos that's what everyone understands. Once calculated 0.25mm would suffice on a TT system I was working on - has to be 6mm min for mechanical reasons as it happens, but if you can calculate the actual size in can be useful.

 

[Manator]

"consumer units and other switchgear assemblies"

Assemblies are made up of switchgear and controlgear,

An RCCB is just one unit.

The beama guide http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwjr15K1jNXKAhVGYg8KHc0WAKwQFggfMAA&url=http%3A%2F%2Fwww.beama.org.uk%2Fasset%2F7DF1EEE0-F314-452B-81E276BC561F4B89%2F&usg=AFQjCNE72N3VpAbRL3dcAKq9ivQ6Ev5oyA does not mention an RCD in an enclosure. The similar switchgear assemblies it says are in scope all have separate units for switching and for control, those not in scope include various RCDs. I fail to see how an RCD in an enclosure needs a metal box.

Rob this is why I read the regulations deeper than most, your link is one I have used for examples of further readings to support my written statements.

I can see where and why you have drawn your conclusion, but you have failed to read the full content.

You are wrong, I will not tell you why, but rather hope that yourself and others will start to read the regulations proper.

I will however give you a clue, just so that I do not come across as a pompous twit, there is a sentence directly after the reason you believe why a RCD in an enclosure does not require to be enclosed in a metal box.

I would also like to dispell the myth that a metal CU should not be used for TT.

 

[Rob_the_rich]

I mis-quoted the reg ""consumer units and other similar switchgear assemblies"

the similar bit is important, an assembly which is similar to a consumer unit.

 

[SPECIAL LOCATION]

I mis-quoted the reg ""consumer units and other similar switchgear assemblies"

the similar bit is important, an assembly which is similar to a consumer unit.

I read it as.....

Anything that could potentially have up to a 25mm2 tail rammed into its terminations "IS Rather Similar".....

Whereas an accessory such as a shower or cooker switch that can only accommodate up to 10mm2 is not!

:Salute