This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Separation of Electrical Supplies

We are installing an air source heat pump into one of our buildings at work, a bivalent system where we are still maintaining use of the existing gas boiler. As a result of the additional electrical load, the building will require an electrical upgrade and in this case it warrants a 500 kVa substation, which is based on feedback from our DNO.

We have liaised with the DNO and they have agreed that a secondary supply can be installed just for the heat pump which will mean that the electrical upgrade will require a feeder pillar for the new supply supply and therefore remove the current requirement for a substation and therefore driving down costs.

However, there are certain proviso's for having a secondary electrical supply and one of these is confirmation of electrical separation between the second (new) supply and the building's existing electrical supply. For this, we can incorporate engineering measures into the design for the heat pump's electrical installation, its controls (use of fibre optics) and the physical pipework (include non conductive break points) as this pipework will travel between both the heat pump out-house and the main building. Although in theory we can confirm electrical separation, one area of concern has been flagged and that is the pipework will be carrying flow and return water from the heating distribution systems (bivalent use: heat pump and existing boiler), and we may not be able to provide a statement of separation to the DNO. 

I was wondering if any members have encountered a similar situation and I would be interested in how they have approached this. The main driver for myself is based on cost and the difference between having a feeder pillar for a second supply to the heat pump installation only as opposed to a substation for the entire building (and heat pump) means that we can potentially save IRO £50,000. 

Parents Reply Children
  • No, as by the time it is impure enough to be a significant conductor it is too contaminated to be safe to drink, but wastewater maybe, depending what is in it. The salt water from water softeners being cycled and swimming pool wastes are two examples that need a bit more thought. Even so by the time the liquid column is longer than a few hundred times its diameter, it is a pretty good resistance.

    Incidentally we use water with controlled doses of washing soda in plastic tubes as fail to safe high voltage bleed resistors in the pulse power lab at work . Very cheap, easy to maintain and a visible indicator of faults.