Calling all Sparks - Replacement CU

[securespark]

Apologies for the less than subtle subject title.

I just want people's opinions on what to specify when replacing a consumer unit.

What are people's views on timelag RCD's, RCBO's etcetera?

Having used mainly bog-standard split-load boards in the past, I wonder if I should start specifying something a bit more sophisticated.

My client wants a replacement consumer unit with the following circuits:

Hob

Oven

Sockets & Garage

Sockets & Central Heating

Water Heater

Freezer - new circuit to be installed to avoid the RCD.

Lights

Lights

Lights

Doorbell

Which circuits would you protect with what device?


Also, the meter is outside and the tails run up through the cavity which is stuffed full of formaldehyde foam insulation AND they are in excess of 3 metres long, which exceeds the EB's guidlines of 2 metres.

 

[Big_Spark]

Hob ......20A/16A 30mA RCBO...dependingn of actual rating of unit.

Oven.....16A 30mA RCBO..Unless Gas

Sockets & Garage....I would split this into two circuits, Sockets on a type B 32A MCB, Garage protected by a suitably rated 30mA RCBO

Sockets & Central Heating..I would split this into two circuits, Sockets on a type B 32A MCB, the Central Heating on a 16A Type B MCB

Water Heater....Depending on type and rating, either an MCB or RCBO of appropriate rating.

Freezer - new circuit to be installed to avoid the RCD. 6A Type B MCB or larger if the circuit to be used for other items, but not exceeding 16A if a radial, unless wired in 4mm2, then not exceeding 25A

Lights...6A Type B MCB

Lights...6A Type B MCB

Lights...6A Type B MCB

Doorbell...3A Type B MCB

Regarding the location of the meter, the way around this is to install a lockable Isolator in the meter cabinet, the meter tails supply this, from the Isolator you use 25mm2 3 core SWA to supply the Consumer Unit directly. The Isolator will not need to be fused, but it may be a good idea as this would blow before the main fuse and would thus not mean calling the Leccy Supplier out..thus saving money. That is is this Guy is into messing about in his house..personal call dependant on the situation.

I would not use an RCD as a main switch as it is uneccessary, a simple 100A DP Isolator is sufficent.

Board recomendations....MEM (Memeera range), MK, Merlin-Gerin or Hager, if locatable at a sensible price, Crabtree is worth a look.

Hager do some nice Vision CU's...they look good and they are good quality now compared to that of several years ago.

 

[securespark]

So why use RCBO's instead of an RCD? They crank up the cost terribly - they're £30-40 each!!

And what about 100mA RCD main switch??

Not that you recommend using one, but as far as I can see from Hager in the dogalogue (!), their incoming RCD's are only rated at 63A...


Take your pont about SWA, but the distance is still a problem, no?

 

[Big_Spark]

So why use RCBO's instead of an RCD? They crank up the cost terribly - they're £30-40 each!!

And what about 100mA RCD main switch??

Not that you recommend using one, but as far as I can see from Hager in the dogalogue (!), their incoming RCD's are only rated at 63A...


Take your pont about SWA, but the distance is still a problem, no?

I know that RCBO's crank the cost up, but they are the more practical solution. Not every circuit requires RCD protection, and in many cases it is not necessary. You could leave the RCBO's off the oven and hob to reduce cost, but I think you need to weight that against the manufacturer.

I would not have a Main Switch RCD unless it was 300mA due to nuisance tripping caused by harmonics etc. Personally I hate RCD main switches, this is not what they were originally designed for and in many cases can be more trouble that their worth.

Hager do make CU's with 100A RCD's. Check out hager , click on Our Products on the left, then click Hager from the menu, then select Vision Consumer Units (2nd one down)

The SWA is not a problem, the Isolator you install in the meter cabinet is connected to the meter by tails, and is therefore the first part of the Customer Installation, this is perfectly safe, within the regs and supply act, and totally acceptable. I would use 3 core as stated, but still use the proper glanding procedure. This would give a really nice earth connection then.

 

[securespark]

J

I have the figures for the cooking appliances:

HOB: 21.74A

COOKER: 20.97A

Both calc'd at 230.

How many of the previous manufacturers make a 25A RCBO?

 

[Big_Spark]

All of them will make 25A RCBO's, although they may for enclosure fitting only, not consumer unit. You may need to go to a 32A.

I know Merlin-Gerin make one for distribution boards, but their website is a pile of excrement.

 

[securespark]

You'd be surprised how many websites are ****e.

Went to one of the big sheds sites today to see what some of their prices were like (I have to compete sadly against clients who say "I can get it for £XX.XX down at *******)

And I typed in two product searches: consumer units and shower trays.

Neither search came back with any relevant goods...

BTW, back onto the tails in the cavity poser. Is it going to be acceptable to run SWA (or DI tails) in a cavity, further, one that is filled with insulation?

 

[Big_Spark]

Simon, The foam insulation may attack DI tails chemically and cause the insulation to harden as plasticiser is leached from it over time. SWA is UV stabilised and treated to prevent chemical reactions with insulating foam and fire retardant chemicals as it is designed for use in hazardous locations.

I know SWA may be a bugger to use, but it is safe, complies with the regs and should be easy to push through the cavity too.

 

[securespark]

The other thing I was getting at was the insulation won't overheat the cable. Also, some say that cables in cavities is not good practice from a damage pov.

 

[Big_Spark]

The other thing I was getting at was the insulation won't overheat the cable. Also, some say that cables in cavities is not good practice from a damage pov.

Unless the potential load is huge, I think the insulation will have little effect on the electrical properties of the SWA, the loading of the cable should handle it, especially over such a short distance.

Cables in cavities are not ideal, but how else will you get from the meter cabinet to the consumer unit?

 

[securespark]

True. Up the outside in galv trunking. Pig's ear!

 

[Big_Spark]

True. Up the outside in galv trunking. Pig's ear!

Personally I would not insult a pigs' ear

 

[securespark]

Spent some time on the dog today, delving into the murky world of RCBO's.

Seems a lot of manufacturers, Wylex included, only make Type C units.

I have found MK and MEM that make Type B. Before I do my nut ringing all the wholesalers, does anyone know who else makes Type B RCBO's?

 

[Big_Spark]

I have found MK and MEM that make Type B. Before I do my nut ringing all the wholesalers, does anyone know who else makes Type B RCBO's?

Hager and Merlin-Gerin make Type B RCBO's..I believe MEM do too..in fact I'm sure they do.

 

[securespark]

Thanks J

Certainly not Wylex!!

Finding it difficult to track down anything other than MEM & MK.

Which 'salers do you use for which boards?