I will go into a little more detail on how 722.311.201 applies to maximum demand and load curtailment, Especially from a Motability point of view, as I’m aware of how the survey is carried out mostly by scheme users. I can’t speak on how this has been done for the FB group, or want to get involved.
Chapter 31 of regulations, talks alot about maximum demand, sec 311.1 mentions how maximum demand should be calculated and where diversity may be considered for the whole or part of the installation.
The installation certificate issued at the time of installation of the Easee charger has a box where the information for maximum demand is put in kVA or Amps. Its unlikely to say how it was calculated. (a pic would be good)
Asessing maximum demand in general and in particular for charge points –
Lets say, for example you have a 10 way consumer unit, which has the following MCB’s 40A cooker, 2x 32A ring circuits (sockets), 16A immersion heater and 2x 6A lighting circuits.
To calculate maximum demand for the above random consumer unit.
40+(0.4*(32+32+16+6+6)) = 76.8A current maximum demand of the home
In other words 100% of the largest circuit plus 40% of the rest.
76.8A is safely within the 100A main switch of the consumer unit and importantly safely within the DNO’s 80 or 100A cut-out fuse.
In order to facilate the installation of a charge point a new 32A circuit will need to be added and most likely a dedicated cconsumer unit for the charger.
A typical 7kW charger is rated at 30.43A, No allowance for diversity is allowed meaning the full 30.43A is taken into acount.
The new maximum demand with the chargepoint connected is now 107.2A (76.8+30.43)
The new maximum demand exceeds the current rating of the consumer units main switch, unless a dedicated consumer unit for charger purposes is installed as is the norm
More so the new maximum demand exceeds the current rating of the DNO’s cut-out fuse and therefore must be refered to the DNO for assessment. The DNO must also be notified if the maximum demand is equall to or greater than 60A, so they can install either a 80 or 100A cut out fuse for 1 phase supplies. However we have a new 107.2A maximum demand, which is greater than the DNO’s cut-out fuse.
The important bit, which refers back to yesterdays post.
In order to reduce the load, load curtailment may be used, which can be used to determine the maximum demand. By far the easiest and most used methods of load curtailment are current clamps (CT clamps)
A current clamp installed with the installation of a charge point will ensure the load is automatically monitored not to exceed the DNO’s cut-out rating or the consumer units main switch will not become overloaded, making an 107.2A maximum demand safe to use and limited to 80 or 100A set by either the DNO’s cut -out or main switch of the consumer unit.
The current clamp works on the principle of reducing the chargers load in the event the whole installation becomes dangerously close to overloading. As more people start using their appliances at night during cheaper rates a clamp will also add an extra level of safety, along with those that get cheaper rates a certain times of the day whils’t charging.
The requirement of regulation 641.2 and sec 30, that an assessment of the electrical installation is provided to the person carrying out the inspection and testing, which includes the installation’s safety and characteristics –
Purpose for which it is intended to be used
Structure and supplies
External influences
Compatibility of associated equipment
All recognised safety services and Assessment for continuity of the services.
etc
Based on these it is vital to asses what used for before commencement of the design process. This is to ensure there are no inherent problems resulting from excessive loading or inadequate protection of the services.
How this can be met by providing a few photos, especially taking into account external influences is beyond me!
