John Rumm wrote:

On 13/11/2017 13:10, whisky-dave wrote:
On Saturday, 11 November 2017 15:10:34 UTC, ARW wrote:

Voltage 202


The fact that the voltage drops to 202V suggests that the wiring is
a little bit suspect.

How ? Surely it's just basic ohms law,

It is... and one should design circuits such that at full load they
still meet the basic requirement of showing no more than 4% or 5%[1]
voltage drop.

Since it does not appear that yours are meeting that requirement, it
would suggest that either the cable run in the circuit itself or that of
the sub main feeding the CU at the origin of the circuit is
underspecified for the length of cable in use.

[1] Used to be 4% on all circuits. These days its 5% on power circuits,
but 3% on lighting circuits.


although the department did
have one of those autotransformers installed a few years ago they are
meant to save money by reducing the voltage slightly I think.

That will make matters worse in this circumstance.

(also not going to help reduce costs either since the heaters will just
need to run longer to provide the required energy transfer).

I thought even on extention leads that the voltage drop increased us
the current went up pretty basic stuff I thought.

Indeed it is.

It seems he already has as much electrical heating as that
autotransformer will ever supply, and is probably exceeding its ratings.
Perhaps someone who knows where it is could have a quick look and see if
any smoke comes out when the voltage drops to 202V?

--

Roger Hayter