Recs for Extension lead please

[Dave Liquorice]

But W will vary with V as R is essentially constant.

If the rating plate says 2200 W @ 230 V the current is 9.6 A and R = V^2/W = 24.04 ohms. Increase the voltage to 240 V(*) the current goes up to 9.98 A.

(*) Our voltage is 240 +/- 5 V unless the local primamry substation is on the back up 11 kV feed instead of the main 33 kV. In which case the voltage ranges over a day from < 230 to > 255. Yes out of tolerance... 255 in the above gives 10.6 A.

I'd recomend that the OP gets a 13 A rated 10 m extension and ensures it is fully unreeled. There might be ones with a resetable thermal cutout, lest he forget...

[Martin Brown]

There is also a significant difference in running a 10A load continuously vs a 10A load for a few minutes every hour or so. The latter puts much less thermal stress on the installation.

It is an important point if you are going to run close to the rated current through a conductor that it must not be still be rolled up. We have had problems before with the church tea ladies using an extension reel to boil 2x 3kW kettles with only about half the cable out. It melted the insulation and internals of the reel before any fuses blew.

All the village hall extension cables now have thermal cutouts on them.

[tabbypurr]

it's not entirely impossible to miswire an immersion heaer so you end up with lots of CPC current. That would create inductance, but still not heating of the coiled extension lead.

NT

[Dave Plowman (News)]

How does a thermal cutout work on an extension? An extension reel, I can understand.

[charles]

the max permitted is 253.0V. Arec younsure your voltmeter is accurate.

[Dave Liquorice]

substation

"max permitted" on paper...

Close enough that the DNO was quite interested in daily plots of voltage whilst the primary was on the back up feed. This was after an engineer had called, seen the plots and measured the voltage which agreed with my reading at the time.

There happened to be other engineers at the 11 kV backup feed orginating primary substation, they gave 'em a call and got that knocked down a notch. That did bring our voltage down to 253 ish but only for about 24 hours. Not overly surprising as the distribution system is a balancing act of transformer tappings, line loss and regulators. Drop the line voltage and everyones voltage drops. There is a regulator in the back up feed and that ought to keep the 11 kV it feeds on to the primary at the correct level.

Looking at the date (2014) on this plot:

I suspect they gave the regulator a hefty kick shortly after the 33 kV was back in use as I've not spotted any serious voltage fluctuations since. We sit at 240 +/- 5 V pretty much 24/7.