A domestic installer is just that and nothing more, they are not fully qualified electrical engineers who know the why as well as the how and would not touch three phase work. They were created to save the property developers from paying the going rate for an electrician as all they wanted was someone who could wire a new build.All the domestic installers I know of wouldn't know what 3 phase was, is this not outside the scope of Part P anyway, what is it they are pricing for? .
They can do domestic work, they have all the test equipment needed for three phase which a domestic installer will not and just need to complete and sign the paperwork. If a domestic installer cannot and also a industrial electrician cannot then who would ?And if I could... I would use the industrial contractors/contacts I have, but alas they are not certified to do domestic installations and it's around 30-40 miles away.
That is very vague for a job description, if it is just a board then that is way to much to pay but if it involves getting a cable provided by the local DNO and then wiring up a workshop for both single and three phase power along with materials then it becomes more feasable.Your assuming a lot here, £7-15k for a board installation...
That is because they do not encounter three phase in domestic properties, do not buy the more expensive test equipment that can handle the higher voltages and potential fault currents plus they are not qualified and would need to get trained as a full blown electrical engineer.Never understood why, but there are not many domestic sparks who deal with 3 phase
You cannot undertake any of the design or installation work which is the responsibilty of the person signing the job off. It sounds like a simple job but there is a lot more involved in order to ensure compliance with the regs and it is safe but 15K does sound steep.The biggest issue I see as I read this is that you are proposing to do a lot of the installation yourself. You imply you will be selecting and installing cables etc before the electrician installs the board. So you are taking design, selection and installation responsibilities on yourself, who I assume have no qualifications to do any of those things.
Cable enters property into the DNO meter / fuses. From meter into a junction box where it feeds one phase and neutral back for the domestic supply. The protective earth will come from the MET which is from the incoming neutral as part of the PME system used in domestic. From the junction box it will feed an isolator which then feeds the workshop board. First decision is how are you going to provide the protective earth in the workshop ? Do have extraneous-conductive components in your workshop construction ? Reg 411.3.1.2 might help.