Upgrade 60A fuse; Crabtree Starbreaker backward-compatible?

[markocosic]

Hello,


Ex council terrace, built sometime between 1950- and 1970. The electrical supply is via a lead sheathed cable entering under the stairs, and the earth is bonded to the lead sheath:

http://www.flickr.com/photos/24994361@N03/8438845557/


The Economy 7 meter is being ripped out on Feb 20th and replaced with a normal single tariff affair. I've picked up a switchfuse (cheaper than an isolator at TLC) and some 25mm^2 tails for the cutout<>meter and meter<>switchfuse runs, and am going to ask the man from the electricity board nicely to connect to those when he changes the meter.

Switchfuse isolator:
http://www.tlc-direct.co.uk/Products/CGMSF100.html


The CU is a "Crabtree Starbreaker" and I've a lovely note and instructions from 1983 to explain what an RCCB is. Mainswitch feeds two 6A lighting circuits wired in 1.0mm^2, a 16A emergency immersion wired in 2.5mm^2, and a 40A cooker wired in 6mm^2. RCD feeds a 32A breaker for shower in 10mm^2, and two 32A ring mains wired in 2.5mm^2.

Kudos to the council for fitting the RCCB when rewiring the house in those days. Less kudos to whomever lost the blanking plates though:

http://www.flickr.com/photos/24994361@N03/8438844289/in/photostream


I'd like to fill that hole. I'd also like to run an electric shower (currently 8.5 kW, but would prefer 10.8kW) and an induction hob (3 zones; max rated input 6.9kW).

Shower:
http://www.plumbplanet.com/product/10068401

Hob:
http://www.aeg.co.uk/Products/Cooking/Hobs/Induction_hobs/HK953400FB


Q1: Are the current "starbreaker" MCBs and blanks backwards compatible? Will these fit the unit pictured?

http://www.tlc-direct.co.uk/Products/CB413slash236565B.html


Q2: Is 40A an appropriate MCB for 6mm^2 cable? It runs in bunched trunking for a metre or so, then inside the ceiling-floor void, and is then buried in the wall. (without trunking; it's an old installation) Is this cable appropriate for the induction hob?

I'm thinking a 32A breaker would be more appropriat, but the cable is ok, based on this TLC calculator:

http://www.tlc-direct.co.uk/Technic...230&length=10&submit=Calculate+Min+Cable+Size


Q3: Will that CU take a 50A breaker for a 10.8 kW shower? Is a 6m run of 10mm^2 cable ok at 10.8 kW? It runs again in mini trunking for a metre, across 2 metres of floor void, then up a cinderblock wall to the attic and 1 metre to the switch.

TLC calculator suggests 16mm^2 but that's pretty darn monstrous, no?

http://www.tlc-direct.co.uk/Technic...=230&length=6&submit=Calculate+Min+Cable+Size

(the 32A breaker is overloaded by the 8.5kW shower as-is; not my doing)


Q4: The cutout is fused at 60A at present. Who do I ask to upgrade that, and is it likely that they will do so or not?


I'll be DIYing then going via LABC for sign-off. (I've got an end gable that needs some lateral support and a chimney to come down and it can all go on the same ticket)


Bonus question: Any idea what the orange taped service is in this photo? Gas yellow and capped is obvious, but orange?

http://www.flickr.com/photos/24994361@N03/8438860671/


Cheers,

--
Marko

 

[streetlighter]

With regard to the Crabtree starbreaker consumer unit the one you have is know as the Sb6000 range these MCBs will not fit the modern units as the new ones use a special plug in busbar system and to be honest are a very good design and well made unit but expensive.
Strip the parts out of the old unit and sell them on eBay the MCBs sell very well as they where a popular unit in the 80/90s and spare breakers are hard to come by.
Them units where fitted in many council houses round where I used to live but they had RCCB incomers and where not split load and often where a skeleton unit installed in the Mantel box.

 

[bernardgreen]

Bonus question: Any idea what the orange taped service is in this photo? Gas yellow and capped is obvious, but orange?

Do you have a gas meter elsewhere in the house ? If not the orange taped service may be the gas supply from the meter to the rest of the house.

I would give some thought to supplying the shower from its own switched fuse and RCB and not from the consumer unit that supplies the lights and sockets. Although it does involve the "single point of disconnection" being the isolator in the meter box it does reduce the load on the CU bus bar and terminals

 

[EFLImpudence]

TLC calculator suggests 16mm^2 but that's pretty darn monstrous, no?

http://www.tlc-direct.co.uk/Technic...=230&length=6&submit=Calculate+Min+Cable+Size

Yes - Keep the cable away from the thermal insulation then it is 6mm²

10.8kW @ 240V which is probably what will be stated on the box is 45A.
equivalent to 9.94kW @ 230V = 43.2A.

 

[TheKeymeister]

Q4: The cutout is fused at 60A at present. Who do I ask to upgrade that, and is it likely that they will do so or not?

You need to speak to your DNO about that, some will just come out and do it, some will ask for you to fill out an increase in supply form.

 

[markocosic]

Q1: Thanks streetlighter, I was afraid of that!

Q3: Thanks EFLImpudence, as aside from the first metre (surface trunking) it's either floating in an uninsulated floor void or plastered (browning, not dot and dab plasterboard) into a wall I'd say it's uninsulated for most of the run and the existing 10 mm^2 will be ample. I'll give it it's own piece of trunking such that it isn't forced to share with other cables.

Q4: Thanks TheKeymeister; I'll probably wait until the meter-changing chappie arrives on the 20th, as the induciton hob won't be fitted until then and it hasn't popped the fuse to date with the current setup.

Bonus question: That could well be it bernardgreen. All the houses here have a fugly meter box "afterthoughted" on the outside of the house. Mine just feeds the boiler, but there are also capped appliance gas pipes in the kitchen (hob) and in the living room (fire). Suspect an old indoor meter under the stairs, next to the leccy. Gas comes up the yellow one, to the meter, then down the orange one and to the kitchen/living room fittings? I'll try the nation grid support line and see if they have any records.

Q2: largely irrelevant if I'm having to change the CU.



Q6: If I were to feed the shower from a separate switched fuse and RCD as bernardgreen suggests, how do I handle the fusing? Does it mean henley blocks for live and neutral, then tee (all still in 25mm^2) to a "consumer unit" and a "mini consumer unit" from there?

Is it really necessary? Any CU I fit now will have two RCDs and an internal split. If I keep the shower MCB right newt to the RCD on the busbar then the loaded length is minimal and it shouldn't be problem, no? (current one works fine as-is)

 

[TheKeymeister]

Q4: Thanks TheKeymeister; I'll probably wait until the meter-changing chappie arrives on the 20th, as the induciton hob won't be fitted until then and it hasn't popped the fuse to date with the current setup.

He definitely won't upgrade your fuse, if that's what you're thinking.

 

[markocosic]

That's what I was thinking.


SSE arranged the meter change over the phone.


UK Power Networks (the DNO) have sent a "small services/application for an electricity connection" form back that covers new supplies and upgrades up to 70KVA, which you send in to get an "estimate of cost" so I'm guessing that fuse will stay at 60A for a while...


This is a house fuse, right?

http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/HRC_Cartridge_Fuse_1/index.html

And these are the curves?

http://wiki.diyfaq.org.uk/images/0/06/Curve-BS1361.png

That says a 60A service fuse will tolerate 100A for 40 minutes. Shower takes "45A" and the hob could take "30A" at absolutely full chat, plus "30A" if there are both microwave ovens and the washing machine on, but that lot isn't going to last 40 minutes continuous so I imagine it'll remain adequate.



On the bonus question regarding gas, I dropped national grid a query on [email protected] and it turns out that:

-they're happy to do a 'live or dead' check on the service pipes free of charge

-they're really quick to respond to email and were happy to arrange this on a sunday evening for tuesday morning

I thought that was really rather helpful.


Starting a new thread on a replacement CU and bonding requirements.

 

[TheKeymeister]

A service fuse will blow at approx 1.5x it's rating, so it should probably hold but you should get it done. They won't start charging you hundreds of pounds to replace a service fuse, it's 5 minutes work usually, as long as it is just that.

They'll want to make sure your service cable isn't undersized, and by just pulling load over the fuse rating, you really don't know what damage you might be causing...

Have you a metal clad cutout? That could wangle you a cutout change free of charge

 

[EFLImpudence]

That says a 60A service fuse will tolerate 100A for 40 minutes. Shower takes "45A" and the hob could take "30A" at absolutely full chat, plus "30A" if there are both microwave ovens and the washing machine on, but that lot isn't going to last 40 minutes continuous so I imagine it'll remain adequate.

The curves are not for you to 'design' in as much overload as you can.

There are also regulations which state that the rating of the protective device must be higher than the design current but I suppose that is inconvenient.

 

[markocosic]

Cutout:

http://www.flickr.com/photos/24994361@N03/8438845557/

Its a hard (bakelite?) plastic. I'll fill in the form they've sent and see what they say.

he curves are not for you to 'design' in as much overload as you can.

Understood.

I was just totting up what was theoretically possible as an "instantaneous" load and checking that the fuse wouldn't pop immediately. Average load is likely to be well below that - showering whilst running 3 pots on full boil and two ovens warming up from cold and the washing machine heating element on is not a typical scenario.

There are also regulations which state that the rating of the protective device must be higher than the design current but I suppose that is inconvenient.

Far from it. Cable rated current > fuse rated current > design current is perfectly sensible.

 

[TheKeymeister]

Cutout:

http://www.flickr.com/photos/24994361@N03/8438845557/

Its a hard (bakelite?) plastic. I'll fill in the form they've sent and see what they say.

Send a copy of the picture in if you can, it might help

 

[EFLImpudence]

BS 951 MET ?

What is the connection below the bottom of the picture?

The Earthing Conductor should go to an earthing block for all the connections and would likely be 6mm² originally.

 

[markocosic]

Yes...

I'm busy writing a new thread with bonding queries as we speak as these need attention.

 

[Taylortwocities]

marcocosic

PLEASE read and follow the instructions on how to show photos in your posts. Its here //www.diynot.com/forums/viewtopic.php?t=129539

Personally I can't be 'rsed to kepp having to access FLIKR and then go back to read the next bit of your post.

If you do as the instruction says then it will be much easier to help you Thanx