Supply requirement for heaters

I urge not calculating with too much precision. If the heater is designed 220 volts, and is connected to 250 volt supply, it will draw significantly more current then calculation suggests.

I urge the use of OCPD and cable rated for 125 amps. Also consider that the heater may be replaced with another of a similar NOMINAL rating, but slightly higher actual  loading, within the lifetime of the electrical installation.

Well the plot thickens! NGrid came out and discovered a brand new LUCY box with 3 x 200A fuses still in their packets ready to go. From this box there are 4 x meter tails in trunking which rises to the next floor. We had a look just before Xmas and found that they enter a metal enclosure equiped with 3 x CTs and associated wiring but with no meter fitted. The tails pass through this box into what was a brand new Square D I-Line Speed D Size I series B panel board equipped with MCCBs of various ratings and an incomer MCCB rated at 180A. NOTE: NGrid said that this supply wasn't even on their asset list and they had no idea it had been put in. My guess at the date of installation is something like 1994.

This opens up a few more possibilities.

We can either, fit a 100A MCCB and run some 35mm 4 core SWA to a suitable outlet for the heater, or, we can go up to say, 50mm 4 core and uprate the MCCB to say 150A, then hang a 4 way TPN dist board at the other end, one way of which can be used for the heater. The latter proposition in terms of costs going forward looks to be more attractive because there is a proposal in the offing to also fit a lift, and a supply will be needed for that, which brings me onto my next question about requirements for lift supplies in general which I will post seperately in another thread.

haha I thought for a brief moment you were going to say the heater was to be fitted to the supply with no meter - it would certainly be cheaper at least in the short term.

30 plus  years is a long time between first fix and second.

Joking aside, its not that uncommon for the DNO records to be incomplete in some way - partly why I take the 'by inquiry' option for PSSC Zs and so on with a pinch of salt - if the measurement disagrees, then it is the book value that is suspect.. 

The most effective way of doing things will depend a bit on the lengths from the new supply and how the DNO/ supplier  wish to play it in terms of billing and metering if it means another MPAN and set of charges.

You have not mentioned anything as mundane as earthing, Is it TNC at the main to the Lucy box and TNC-s thereafter, and how are the other supplies in the building. (trying to avoid high cross section earth bonds.)

Mike.

haha I thought for a brief moment you were going to say the heater was to be fitted to the supply with no meter - it would certainly be cheaper at least in the short term.

30 plus  years is a long time between first fix and second.

Joking aside, its not that uncommon for the DNO records to be incomplete in some way - partly why I take the 'by inquiry' option for PSSC Zs and so on with a pinch of salt - if the measurement disagrees, then it is the book value that is suspect.. 

The most effective way of doing things will depend a bit on the lengths from the new supply and how the DNO/ supplier  wish to play it in terms of billing and metering if it means another MPAN and set of charges.

You have not mentioned anything as mundane as earthing, Is it TNC at the main to the Lucy box and TNC-s thereafter, and how are the other supplies in the building. (trying to avoid high cross section earth bonds.)

Mike.

Upper level LUCY box looks to have a seperate earth run from the neutral termina into the panel board so most liklely TNC-S. Not seen inside the lower LUCY box where the incoming supply cable pops in from the road but there are only 4 x TPN tails conductors leaving this box which rise to the second LUCY box on the 1st floor so bottom box must be TNC. Am guessing tails size is either 35mm or 50mm. Must have a look at size stamped on cable lugs to find out.

Am assuming they are now shopping round for a competitive supplier/meter company or whatever. Supply is de-enrgised at bottom LUCY box with 200A fuses remaining in their packing until someone comes out to fit.