Thoughts on Commando + Ohme as Home Charging Option

[Glan gluaisne]

A friend of mine can’t get the £500 OLEV grant so was looking for cheaper alternatives to buying a wall charger. Her local electrician charges £40 for the first hour and £20 for every subsequent hour. She bought this socket (I think it’s this one):

Industrial RCD Socket IP67 240V 32A 30ma 2P+E Switched

Total materials were £110 and electrician was £60. Rather than using the UMC supplied with the car she bought her own - that was the most expensive bit. But she’s now charging at 32A and is a happy bunny.

Only two things to watch with this option is that, as the commando is being used primarily as a car charge point, it needs to be installed in accordance with the slightly different regs in Section 722 of BS7671:2018 (so needs an earth electrode, Type A RCBO, etc, and must not connect to the houseTN-C-S/PME PE) and the installation probably needs to be notified to the DNO (debatable as to whether the latter applies, but I suspect it may).

Many electricians may well not be aware of these requirements, as they wouldn't normally apply to a commando outlet installation for most other purposes.

 

[Artiste]

Only two things to watch with this option is that, as the commando is being used primarily as a car charge point, it needs to be installed in accordance with the slightly different regs in Section 722 of BS7671:2018 (so needs an earth electrode, Type A RCBO, etc, and must not connect to the houseTN-C-S/PME PE) and the installation probably needs to be notified to the DNO (debatable as to whether the latter applies, but I suspect it may).

Many electricians may well not be aware of these requirements, as they wouldn't normally apply to a commando outlet installation for most other purposes.

I'm pretty certain that her commando socket was installed to pre 18th Edition regs. She didn't say it was for charging an EV and the electrician didn't ask. As well as having an RCD in the socket it's also wired into a dedicated mini consumer unit with a 32A MCB in the house. Given that it's considered safe for any other use, and given that she is the only person who will be using it (except perhaps me when I'm visiting) she's willing to take the risk.

 

[Glan gluaisne]

I'm pretty certain that her commando socket was installed to pre 18th Edition regs. She didn't say it was for charging an EV and the electrician didn't ask. As well as having an RCD in the socket it's also wired into a dedicated mini consumer unit with a 32A MCB in the house. Given that it's considered safe for any other use, and given that she is the only person who will be using it (except perhaps me when I'm visiting) she's willing to take the risk.

Even before the 18th came out, there was a requirement for an EV charge point, or a connection intended to be used for charging an EV, to not be connected to a TN-C-S/PME PE, but to be connected as a TT island, with an earth rod. It was widely ignored, though.

 

[MrBadger]

Am I right in hearing that is because there are many hundred reported faults per year of TNC-S earths (or whatever is the common one) not being connected so in event of a fault when charging the car, everything would go straight to ground via what/who ever is common between car and earth?

 

[Glan gluaisne]

Am I right in hearing that is because there are many hundred reported faults per year of TNC-S earths (or whatever is the common one) not being connected so in event of a fault when charging the car, everything would go straight to ground via what/who ever is common between car and earth?

TBH I've not come across many faults on the supplier side or CU incoming PE. I've seen a few slightly loose connections, but they would probably still have been OK in terms of accepting enough fault current to trip any protective device without too much of a potential rise on the earth at the connected equipment. Every time an installation is periodically inspected the incoming PE will be disconnected from the earth bus bar in order to measure Ze, so that may be a reason why such faults aren't often seen; this connection tends to get re-tightened fairly regularly (or does for those who bother to comply with the requirement to have their installation periodically inspected!). I've seen loads of poor or missing CPCs on outlets and appliances over the years, that's so common that I'm surprised that there aren't more accidents. Maybe because a lot of appliances now are Class II, so don't need a CPC connection at all.

An alternative to the need for an earth electrode and TT island for the charge point installation is to install/provide a Type B RCD/RCBO or equivalent level of protection. The house TN-C-S/PME PE can then be used to protect the charge point, with no need for an earth electrode. The main snag with that is that a Type B RCD/RCBO is very expensive, over £200 last time I checked. The specific section of the regs that gives all the options for wiring a charge point, or an outlet to be used for regular EV charging is this bit, may be of interest:


BS7671 18th Ed Section 722.pdf

 

[MrBadger]

My plan is to get this dedicated CU installed in the garage by a local electrician to connect to my TMC and a backup commando and 13A socket. So that hopefully covers the Type B RCD and then its up to the electrician to work out the rest. However, even some Tesla approved installers seem oblivious to the regs so I need to keep a close eye on what the electrician decides on fitting especially they will not be specialist in connecting EV charge points.

 

[Glan gluaisne]

My plan is to get this dedicated CU installed in the garage by a local electrician to connect to my TMC and a backup commando and 13A socket. So that hopefully covers the Type B RCD and then its up to the electrician to work out the rest. However, even some Tesla approved installers seem oblivious to the regs so I need to keep a close eye on what the electrician decides on fitting especially they will not be specialist in connecting EV charge points.

I think that being unaware of either the rules that applied before these were formalised when the 18th came out, or those in the 18th, Section 722, is pretty commonplace amongst electricians who aren't regularly installing charge points. Even some of the approved charge point installers weren't following the rules for years, as the need for either DC-capable residual current detection, or the use of an RCD with a limited DC capability plus an earth electrode has been in the code of practice (which must be adhered to by all OLEV approved installers) for years, long before the 18th came out.

FWIW, my charge point now includes one of these modules: DC/AC Residual Current Sensor - Stegen Electronics an RCM14-03, that provides the required AC and limited DC leakage detection capability and turns off the supply using the contactor in the charge point. I suspect other charge points may use something similar now.