dual row 17th cu ?

[ban-all-sheds]

There have been fierce debates over this in the past. In my opinion, having two DBs doesn't make it two installations. Others disagree and I have no desire to try and change there minds.

Well - maybe one of those who disagrees could try and change your mind, from wrong to right.

Go and read the definition of Electrical Installation in Part 2.

 

[ban-all-sheds]

Each CU would have a main switch, so each installation would have a means of isolation.

There have been fierce debates over this in the past. In my opinion, having two DBs doesn't make it two installations. Others disagree and I have no desire to try and change there minds.

If you want to hedge your bets, go for a single main switch for isolation. This also reduces the size of each DB required

537.1.4 anybody ?

You can go and read the definition in Part 2 as well....

 

[RossR]

I've read the definition in part 2. I've read the arguments both ways and I've reached a decision I'm happy with. I don't go near industrial or commercial. To me 1 dwelling = 1 installation.

 

[ban-all-sheds]

That's not what the regulations say.

It may well be what you imagine them to say, or want them to say, but your imaginative desires don't change what they actually say.

And this:

Don't forget you need a single means of isolation for the whole installation.

is false.

By all means tell the OP that you would like him to have a single means of isolation for all of his CUs, but don't tell him he needs one.

 

[RossR]

Why do dual RCD CUs also have a main switch?

 

[londonboy]

For the sake of an extra £10 its pointless having this debate.

 

[OwainDIYer]

It's unrealistic to expect a single switch to isolate an entire building.

I never mentioned "entire building". I don't think it's unrealistic to expect a single switch to isolate an entire dwelling though.....

That's my opinion. You might disagree, and you're free to, but I think it's safer.

I think for a dwelling a 'single point of isolation' i.e. Big Main Switch is both realistic and safer. A lot of people have problems understanding how circuits work but can just about understand Big Main Switch turns everything off.

Although often omitted where storage heaters are used, with two CUs and no Big Main Switch, the increasing use of combination storage/panel heaters with a daytime peak supply means there's an increasing risk of people turning off the off-peak CU and not realising the heaters are still live.

If Wylex would just make a REC2 isolator with dual outlet terminals so a Henley block wasn't needed as well ...

 

[RF Lighting]

It's unrealistic to expect a single switch to isolate an entire building.

Why would that be ?
I can understand your statement on an older install, but definately not a problem on a new one.

So what about installations in huge commercial premises and the like?

What about them?

I was on a job about a week ago which had a 1600A TP ACB fitted as the main incommer. That's a single point of isolation.

 

[ricicle]

Each CU would have a main switch, so each installation would have a means of isolation.

There have been fierce debates over this in the past. In my opinion, having two DBs doesn't make it two installations. Others disagree and I have no desire to try and change there minds.

If you want to hedge your bets, go for a single main switch for isolation. This also reduces the size of each DB required

537.1.4 anybody ?

You can go and read the definition in Part 2 as well....

537.1.4 Second sentance, first word.

 

[Spark123]

It's unrealistic to expect a single switch to isolate an entire building.

Why would that be ?
I can understand your statement on an older install, but definately not a problem on a new one.

So what about installations in huge commercial premises and the like?

What about them?

I was on a job about a week ago which had a 1600A TP ACB fitted as the main incommer. That's a single point of isolation.

I know of many industrial situations which a single building may be fed from a number of substations, no single point of isolation (and it probably wouldn't be a good idea to have one).
Imagine how it would go down in a hospital if someone pressed the big red button

 

[ban-all-sheds]

537.1.4 Second sentance, first word.

It is "A".

As is the first word in 430.3. Do you think that that regulation means that you're only allowed one protective device?

Go and read all of 537.1.4, second sentence, again - maybe it will dawn on you that what it's saying is that a main switch intended for use by ordinary persons etc shall be a DP device, not that you may only have one such switch.

Did you go to the same school as stoday?

 

[ban-all-sheds]

If you put isolation after some henley blocks then how do you work on those henley blocks? The DNO fuse won't count, as it doesn't interrupt the neutral.

If you put it before, how are you going to work on the tails from the meter that you need to put into the switch?

Why do dual RCD CUs also have a main switch?

Because the RCDs, MCBs, RCBOs in a self-contained CU, and the circuits originating there, constitute an assembly of associated electrical equipment having co-ordinated characteristics to fulfil specific purposes.

 

[RossR]

If you put isolation after some henley blocks then how do you work on those henley blocks? The DNO fuse won't count, as it doesn't interrupt the neutral.

If you put it before, how are you going to work on the tails from the meter that you need to put into the switch?

That's a problem, but by putting it before you are doing a better job of complying with 132.15.1. That's why 537.1.4 says "as near as practicable to the origin" - i.e. as early as practically possible, so to isolate as much as practically possible.

Why do dual RCD CUs also have a main switch?

Because the RCDs, MCBs, RCBOs in a self-contained CU, and the circuits originating there, constitute an assembly of associated electrical equipment having co-ordinated characteristics to fulfil specific purposes.

How does that change when the same protective devices are housed in multiple enclosures?

 

[RossR]

 

[ban-all-sheds]

That's a problem, but by putting it before you are doing a better job of complying with 132.15.1. That's why 537.1.4 says "as near as practicable to the origin" - i.e. as early as practically possible, so to isolate as much as practically possible.

I see we still have the problem that you will not recognise that a house with 2 CUs has 2 installations.

How does that change when the same protective devices are housed in multiple enclosures?

You then have multiple assemblies of associated electrical equipment having co-ordinated characteristics to fulfil specific purposes, and need multiple main switches as per 537.1.4, one for each installation.