Sanity check on plan for CU replacement (MCB to RCBO AFDD)

[j0hnnn]

I'm planning a replacement for my existing domestic CU and would like to have it sanity checked before I get an electrician involved. The main reason for replacing the whole CU is that I would like to have an additional circuit to the attic which would be isolated from the existing one. Long story short, I've got a server rack up there which is increasing in power consumption and had a trip when a computer on the same circuit got powered on. Second reason is that the current CU is using MCBs and also there is no more space left. Instead of planning for another smaller CU, I want to get this done properly and modernised.

Existing Setup

The existing CU is 14-way (all used up). The main fuse from the supplier is 60A.

• CPN IS2100 Isolater Switch (100A) - 100A, 2 Pole. | CPN Cudis - https://cudis.co.uk/product/100a-2-pole/
• 3x CPN MC110B MCB (10A) - 10A - B Curve | CPN Cudis - https://cudis.co.uk/product/10a-b-curve/
• 3x CPN MC116B MCB (16A) - 16A - B Curve | CPN Cudis - https://cudis.co.uk/product/16a-b-curve/
• 4x CPN MC132B MCB (32A) - 32A - B Curve | CPN Cudis - https://cudis.co.uk/product/32a-b-curve/
• 1x CPN RC263/030 RCD (63A) - 63A 30mA Type B | CPN Cudis - https://cudis.co.uk/product/63a-30ma-type-b/

Upgrade Plan

I have spent the last few weeks researching everything electrical related to CUs and tried to incorporate as much of the recommendations I have read online. Since I'm not an electrician, the following is likely to not make sense, completely wrong or "overkill", hence me seeking advice. I fully understand that this plan may require rewiring and won't be cheap so money isn't going to be the significant deciding factor here.

Having looked into the different brands, I'm have made the decision to go with Hager. As mentioned previously, my immediate requirement is to have a new circuit to the attic but would be looking to have an EV charging point installed in the future. So my thought is to get the main supplier fuse upgraded. If I'm reading correctly, going form 60A to 80A could be simple but going to 100A would require a service head replacement. Also, if the cabling into the home isn't adequate, there will be extra work involved. Ideally, I get the main supplier fuse upgraded from 60A to 100A giving me more flexibility for the future. I want to get an isolation switch installed at the same time as there currently isn't one between meter and the CU. I guess I just need to get in touch with my DNO to see what they can do and whether the tails need upgrading too.

For the new CU, I'm considering the following:

• Hager VM120K CU Enclosure (20-way) - VM120K | Hager UK - https://hager.com/uk/products/h/vm120k-conunitd3020w100asw-discknockouts
• Hager VME02SPD SPD Type 2 - VME02SPD | Hager UK - https://hager.com/uk/products/h/vme02spd-cu-surge-protection-kit-type-2
• Various RCBO AFDDs:
  • Hager ARR910U (10A) - ARR910U | Hager UK - https://hager.com/uk/products/h/arr910u-rcbo-with-arc-detect1m-10a-b-6ka-a-30ma
  • Hager ARR916U (16A) - ARR916U | Hager UK - https://hager.com/uk/products/h/arr916u-rcbo-with-arc-detect1m-16a-b-6ka-a-30ma
  • Hager ARR932U (32A) - ARR932U | Hager UK - https://hager.com/uk/products/h/arr932u-rcbo-with-arc-detect1m-32a-b-6ka-a-30ma

With this in place, I'm hoping to have a second circuit installed in the attic purely for the server rack. Currently it's powered using a single socket to a 13A PDU. Maybe I can separate the load here across two PDUs plugged into two different 13A fused sockets from the new circuit, at least I should have more options. I've looked into commando sockets but like I said, unlikely I'll have a load that would warrant it.

So, how does this all sound?

 

[pc1966]

Long story short, I've got a server rack up there which is increasing in power consumption and had a trip when a computer on the same circuit got powered on.

How big are you planning this rack to be?

Are you using a UPS on this?

Generally computer racks can be quite leaky, more than the ~9mA max recommended for your usual 30mA additional protection RCD/RCBO used for general circuits.

If that is the case then hard-wiring the UPS supply without RCD on its input using a suitably protected cable like SWA to a FCU or similar, possibly with supplementary bonding to the rack, would be a better idea. Any RCD protection on sockets fed from the UPS ought to be on its output, say via an RCD FCU (or two, if splitting a lot of low power but leaky loads) to some block(s) of 13A or 10A IEC outlets..

Disconnecting the input to a UPS does nothing to protect some poor sod on its output!

 

[plugsandsparks]

To answer the Ops question - how would an electrician react to the home owner specifying the Cu design ?
TBH - it has never happened, lol
There is no brand loyalty, as such, it is just some brands have quirks in their products that grind your gears when you have to deal with them. I tend to settle on a brand that is supported by local wholesaler, a brand that does not have a key part in short supply, a brand whose quality of housing and fasteners is dependable and strong. Lastly a brand that supports options i may need, its very different in the commercial world, so i tend to be more brand conscious in commercial and industrial. Domestic, you have slightly different priorities.

I think the question may be more relevant to ask yourself how you are likely to react when the electrician proposes a different solution which you have spent hours of research on. Dont expect an electrician to engage in a lengthy conversation, we are not research bods, we are a trade with years of experience in both installations and fault finding / maintenance, this all comes into play when designing any solution.

E.g. I would recommend to get a quote for your installation upgraded to 100A , you may be lucky. A good strong CU housing, the bigger the better, over-size it by at least 20% from what you know today. All RCBO with DP switching, earthing system checked for best possible ZE. SPDs - cheap enough but need to be checked regularly, AFDDs if you really want them but i personally am in no rush to fit them in my own home, could be useful for an electric shower cct, car charger cct or any long duration high power loads.

 

[timhoward]

Also, if I'm replacing the MCBs and I have the option to go for RCBOs or RCBOs with AFDD, if money isn't a big factor, would you still settle just for RCBOs?

I've read this quite quickly, but I'll throw in that while Hager are excellent, unlike other brands their RCBO's only switch the live, not the neutral.
(Also beware that CEF say Hager Single Pole and Neutral, but they aren't, as the photo shows )

So I'd rather have the highly expensive Hager AFDDs or a lesser brand with RCBOs that switch both poles.

If it were me and I was splashing out I'd go the Crabtree route myself. I actually installed Fusebox in my own house but that is because no one was paying me to do it....and I think their perfectly adequate.

 

[j0hnnn]

Chances are we'll see boards filled with AFDDs in the not too distant future, but I'd expect they'll be considerably less expensive by then and possibly more refined. With brands like Hager or Crabtree, it's very likely that availability won't be an issue in the future as both have a great track record where backward compatibility is concerned.

That's a good point. It certainly feels risky opting for what's essentially a new product which most likely can be refined and be cheaper. Given all the feedback so far, I'm now on the fence of going all out AFDDs here, especially since this isn't going to be my final home.

How big are you planning this rack to be?

Are you using a UPS on this?

It's 20U, mostly networking gear with a few servers that could theoretically pull up to 700W individually but idle is around 100W and average during moderate use has been around 150W - 200W. So it's not really a that big considering how big and power hungry racks can be so I haven't planned in anything complex for power here other than the two PDUs (one IEC outlets and other standard UK). Up until recently, the PDUs came off the an APC UPS that had its battery fail so I'm still looking at options to replace that but on hold until I figure out what I'm going to do with the new CU/circuit. Currently, everything is powered off the mains socket. Nothing running is mission critical and everything is backed up (3-2-1) so I'm pondering whether I'll need a UPS again with proper protection in place.

E.g. I would recommend to get a quote for your installation upgraded to 100A , you may be lucky. A good strong CU housing, the bigger the better, over-size it by at least 20% from what you know today. All RCBO with DP switching, earthing system checked for best possible ZE. SPDs - cheap enough but need to be checked regularly, AFDDs if you really want them but i personally am in no rush to fit them in my own home, could be useful for an electric shower cct, car charger cct or any long duration high power loads.

Yea, hopefully going from 14 to 20 ways is enough for what I'll be needing as long as I'm in this house. Already struggling to find space where the existing CU is to replace with something bigger so will potentially need to a new mounting board above the current one, I'll leave this up to the electrician to figure out though. Are earthing system checks for ZE standard part of CU installs or is this something I would have to request the electrician carry out?

I've read this quite quickly, but I'll throw in that while Hager are excellent, unlike other brands their RCBO's only switch the live, not the neutral.
(Also beware that CEF say Hager Single Pole and Neutral, but they aren't, as the photo shows )

So I'd rather have the highly expensive Hager AFDDs or a lesser brand with RCBOs that switch both poles.

This is the unfortunate thing. I had this all planned out with AFDDs which are single module double pole and neutral. As you say, their RCBOs are not, although, their commercial breakers are DP (ADA932U | Hager UK - https://hager.com/uk/products/h/ada932u-rcbo-1pn-6kab-32a-30ma-a) but then at this point it's even more excessive, double module and I would be better off AFDDs with regards to protection and cost.

So, with all the feedback so far, it's clear this is a pretty excessive and an overly risk averse setup for what I'd consider is a "typical home" then I'm back to the drawing board again to consider what my options are for high quality DP RCBOs... Schneider? I've not really came across Crabtree but there seem to be a lot of positive chat about them in this thread so far.

 

[pc1966]

Are earthing system checks for ZE standard part of CU installs or is this something I would have to request the electrician carry out?

They should be. Checking the supply Earth nature & quality, and bonding of extraneous parts like service pipes, would be an essential aspect of any change to a CU, let along complete replacement.

 

[pc1966]

In terms of the rack, even if you just plan on plugging it in to a 13A socket then better to have a single point (single or double socket, 16A/20A) radial just for it.

That way you don't have to deal with leakage on other circuits contributing to any nuisance tripping of the supply, and if it proves to be trip-happy due to the accumulation of all stuff in the rack, you know that is the reason.

 

[j0hnnn]

In terms of the rack, even if you just plan on plugging it in to a 13A socket then better to have a single point (single or double socket, 16A/20A) radial just for it.

Yea, agreed, this was the whole reason behind this installation, to get the rack on its own circuit. Any issue making this a 32A circuit?

I'm going to start reeling it back on the AFDDs though, maybe have this new circuit, shower and garage with them and rest on RCBOs. Although, as I mentioned previously, Hager RCBOs are single pole so I might have to just settle for another brand that the electrician will recommend.

 

[littlespark]

Approach a few electricians and get more than one quote. Make sure they understand you want extra space for future works.

Don’t go for the first name that appears on mybuilder or checkatrade…. In fact… steer clear.

Best option is word of mouth recommendations from friends and neighbours.

 

[pc1966]

Yea, agreed, this was the whole reason behind this installation, to get the rack on its own circuit. Any issue making this a 32A circuit?

Easy to do, just heavier cable, etc. But why?

• If it is a single 13A socket then 13A is max.
• If double then typically they are rated at 20A between the two.
• If you are actually using much more than 13A on your IT kit you will have both an eye-watering electricity bill, and a need for A/C to keep the area cool.

I'm going to start reeling it back on the AFDDs though, maybe have this new circuit, shower and garage with them and rest on RCBOs. Although, as I mentioned previously, Hager RCBOs are single pole so I might have to just settle for another brand that the electrician will recommend.

While you get AFDD in all sorts of ratings, for now the main push has been to have them on socket outlet circuits, presumably because of more risk from arcing from damaged cables / plugs / etc. Inspecting and testing your appliances ("PAT testing") might give you better prevention for the money.

Anecdotally the higher risk of overheating has been high power circuits like cookers & showers that were badly installed so terminals incorrectly tightened and/or poor quality or inappropriate parts used. Often they don't arc as it is basically just a high resistance contact.

RCD/RCBO provide a lot of the protection for general cable damage due to rodents, crushing, nailing, etc., that could cause a fault that creates heat but is not "hard" enough to trip the over-current protection, and so go some way towards reducing the fire risk anyway. With RCBO you find our which circuit is faulted quickly, and don't get healthy ones tripping as well. Also less risk of nuisance tripping as less accumulation of leakage as less appliances per circuit.

Finally, I guess you have a good interlinked smoke alarm system (like Aico, etc)? That is probably a far more important safety aspect then AFDD versus RCBO!

 

[pc1966]

Best option is word of mouth recommendations from friends and neighbours.

The OP might find someone on here that is close enough and already knows the discussion. Some general location like town or (part) postcode (not actually address) would help!

 

[j0hnnn]

If you are actually using much more than 13A on your IT kit you will have both an eye-watering electricity bill, and a need for A/C to keep the area cool.

Yea, true, I figured if I'm getting a new circuit, why not just do 32A in case it gets repurposed later but there is still going to be the existing ring so 20A for a double socket should more than suffice.

Finally, I guess you have a good interlinked smoke alarm system (like Aico, etc)? That is probably a far more important safety aspect then AFDD versus RCBO!

Of course, using (unfortunately) FireAngel Pro Connected and tested regularly. Interestingly and somewhat related to this thread, when I first moved into this home, I wanted to install Aico products but was told this was excessive and FireAngel would be fine so I took the advice. Lessons learned and here we are.

The OP might find someone on here that is close enough and already knows the discussion. Some general location like town or (part) postcode (not actually address) would help!

I actually know a few local people that have done work for friends and family that come recommended so will be able to discuss this installation with them. I just didn't want to approach them initially because as someone said on this thread, they don't really want to get into discussions and are busy as it is.

 

[nicebutdim]

Of course, using (unfortunately) FireAngel Pro Connected and tested regularly. Interestingly and somewhat related to this thread, when I first moved into this home, I wanted to install Aico products but was told this was excessive and FireAngel would be fine so I took the advice. Lessons learned and here we are.

One expensive option that few here would talk anyone out of.

 

[pc1966]

Yea, true, I figured if I'm getting a new circuit, why not just do 32A in case it gets repurposed later but there is still going to be the existing ring so 20A for a double socket should more than suffice.

20A for general purpose sockets is usually considered adequate for 50 m^2 of area so even on its own it could be extended to other outlets up there.

For 32A then (from memory) a radial circuit for 75m^2 and RFC for 100m^2, with the difference down to the acceptable cable lengths at sane cable sizes for voltage drop, as much as anything else.

 

[j0hnnn]

Thanks! So what would be my other high quality/reliable options if I were to just stick to RCBOs and given that Hager ones are single pole?

 

[westward10]

It isn't relevant they are single pole.