CSU Cabling

[iwonbigbro]

Hi,

I bought a new CSU with a load of MCB's (B32s, B16s, B10s and B6s). I have connected up the MCB's to the bus coming from the RCD, but just wondered what gauge cabling I need to use for the neutral connections from the RCD and live connection to and from the main switch and RCD? I only got one cable with the housing that connects the main isolator to the neutral bus, so wonder if there is a kit I can buy from MK that has the appropriate cables included already cut to length and finished with flat caps either end.

P.S. I am preparing the unit for an electrician to install and certify, doing this part myself will save me some considerable labour costs. In hindsight, I should have purchased a ready configured unit.

 

[electronicsuk]

P.S. I am preparing the unit for an electrician to install and certify, doing this part myself will save me some considerable labour costs. In hindsight, I should have purchased a ready configured unit.

It wont save you anything, as the electrician will have to remove all the MCBs again in order to properly run and dress the cables inside the CU.

 

[LoveRocket]

What is a "CSU"?

 

[PrenticeBoyofDerry]

constant speed unit

 

[iwonbigbro]

P.S. I am preparing the unit for an electrician to install and certify, doing this part myself will save me some considerable labour costs. In hindsight, I should have purchased a ready configured unit.

It wont save you anything, as the electrician will have to remove all the MCBs again in order to properly run and dress the cables inside the CU.

Why (when drawing up the quote) did he suggest that I should have bought a ready built unit?

 

[iwonbigbro]

What is a "CSU"?

Don't know why, but MK and Wylex seem to abbreviate their [C]onsumer nits to CSU in the product description on various sites. Have no idea what the S might be, but just wanted to be anal about the description.

 

[PrenticeBoyofDerry]

Why (when drawing up the quote) did he suggest that I should have bought a ready built unit?

You still need to terminate the lighting and power circuits in to the unit, a built up unit means that it is already loaded with MCBs, RCDs, RCBO's etc....not connected to circuits,

 

[iwonbigbro]

Why (when drawing up the quote) did he suggest that I should have bought a ready built unit?

You still need to terminate the lighting power circuits in to the unit, a built up unit means that it is already loaded with MCBs, RCDs, RCBO's etc....not connected to circuits,

I thought these get terminated on the neutral bus? e.g. Ring leaves the breaker to the house with + on breaker and - on neutral bus, ring returns from house with + on second breaker and - on same neutral bus? I thought the point of a ring was to allow the current to be drawn from both ends of the ring?

With this in mind, I don't see what the issue is here?

BTW, lighting ring is being left on the old fuse box because the lighting ring is not earthed. I don't currently have the funds to replace the existing lighting wiring throughout the house to incorporate earth to all the switches, so keeping the existing fuse box for the lighting bypasses the legislation that stipulates a requirement for inclusion of earth on lighting rings when replacing the CU.

 

[electronicsuk]

Why (when drawing up the quote) did he suggest that I should have bought a ready built unit?

You still need to terminate the lighting power circuits in to the unit, a built up unit means that it is already loaded with MCBs, RCDs, RCBO's etc....not connected to circuits,

I thought these get terminated on the neutral bus? e.g. Ring leaves the breaker to the house with + on breaker and - on neutral bus, ring returns from house with + on second breaker and - on same neutral bus? I thought the point of a ring was to allow the current to be drawn from both ends of the ring?

I'm afraid you misunderstand the ring final circuit, but let's clear up the fundamentals first. There is no + or - on the mains supply to your house, only Line and Neutral. Positive and negative are terms reserved for when referring to Direct Current, rather than Alternating Current/AC.

Secondly, both legs of the ring terminate in the same breaker. I.e. both neutrals to the neutral bar, and both lines to a single breaker.

With this in mind, I don't see what the issue is here?

The issue is that it's near impossible to work in these units without removing the breakers first to dress the cables. Therefore, you are completely wasting your time trying to fit anything beforehand. I also think your electrician may have been a little short sighted in recommending you buy a ready-built unit, as there's no guarantee the breakers included in the package will suit your circumstances.

BTW, lighting ring is being left on the old fuse box because the lighting ring is not earthed. I don't currently have the funds to replace the existing lighting wiring throughout the house to incorporate earth to all the switches, so keeping the existing fuse box for the lighting bypasses the legislation that stipulates a requirement for inclusion of earth on lighting rings when replacing the CU.

Lighting is usually installed on a radial circuit. While any new circuits or extensions to the existing wiring should contain an CPC/earth conductor, you can continue to operate your old circuit without an earth as long as there are no class I metal fittings on the circuit. Assuming the cable is PVC and in sound condition, I see no reason it should not be connected to the new CU, and the lack of CPC be noted as a departure.

 

[PrenticeBoyofDerry]

you still need to get your line earths and neutrals from circuits, this will often mean with space constraints that the MCBs need removing for ease of installation but a link to what I believe you need.
http://www.screwfix.com/prods/51990...its/MK-Consumer-Units/MK-Split-Load-Cable-Kit

 

[iwonbigbro]

Okay, understood. Thanks for the link.

It might be the metal light switches that cause the issue with the lighting ring. I suppose if I replace the metal switches with PVC switches, it can be moved over.

 

[electronicsuk]

Okay, understood. Thanks for the link.

It might be the metal light switches that cause the issue with the lighting ring. I suppose if I replace the metal switches with PVC switches, it can be moved over.

Even with the old consumer unit, there still shouldn't have been any metal switches fitted. I assume they aren't original and have more than likely been fitted by a have-a-go DIY'er in the past?

 

[iwonbigbro]

Okay, understood. Thanks for the link.

It might be the metal light switches that cause the issue with the lighting ring. I suppose if I replace the metal switches with PVC switches, it can be moved over.

Even with the old consumer unit, there still shouldn't have been any metal switches fitted. I assume they aren't original and have more than likely been fitted by a have-a-go DIY'er in the past?

Yes

 

[iwonbigbro]

Haven't mentioned the 30 amp oven with hob and dishwasher spur either, just to give you a better picture.

There is one 30 amp feed to the kitchen for the oven with no return. This has then been spurred for the hob to a separate switch, to which the dishwasher has been connected (bodge style). To top it off, you get a lovely tingling sensation if you touch metal parts on the hob and dishwasher together, so I assume some kind of short is occurring that forms a circuit between the dishwasher and hob earth terminals. Nice!

To be honest, I am thinking the rewiring route isn't such a bad solution, since it will identify any other bodges that have been made. Another I can think of is a typical junction box made from electrical tape that was connected to the bathroom light. I need to replace this with a proper junction box when I install new lights in the bathroom.

 

[LoveRocket]

To top it off, you get a lovely tingling sensation if you touch metal parts on the hob and dishwasher together, so I assume some kind of short is occurring that forms a circuit between the dishwasher and hob earth terminals. Nice!

Erm, no. That will be because one of them has an internal fault causing the casing to become live, but also is not earthed properly thus there is no fault current to blow the fuse.

This is serious sh1t and will kill you or a family member if you don't get it fixed ASAP. Why on earth are you continuing to use appliances that give you electric shocks?