So how much power does an oil filled radiator actually use.

[ARW]

So it does.

[ARW]

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

[John Rumm]

So that it is clear for everyone, give an example.

(see what I did there?)

[Johnny B Good]

I did. However, since it implies "Just so" as the starting words, it's a sloppy example. Close but no cigar. :-)

So after all this searching for valid examples, we seem no closer to finding any more than that excellent "So What?" example above (see what I did *there*?). :-).

Just so I can get back to the question raised by the OP[1], I feel I should mention that my own oil filled radiator, a 2.5KW SilverCrest example bought last year from Aldi/Lidle, uses a 4 position rotary selector switch to provide heating levels of zero (off) 800W, 1200W and

2000W, all under the control of an adjustable thermostat. Furthermore, in addition to the oil heating element power level options, it includes a 500W fan heater not controlled by any thermostat other than by the standard overheat cut out stat which is operated independently of the oil heater circuitry by a simple on/off switch with its own neon indicator.

The plastic power level selector and thermostat control knobs have a smooth satin finish which makes the power selector switch awkward to operate for lack of 'grip'. It is notable that the (10A rated) 2 metre Silicone rubber mains lead becomes a little warmish only after switching on the fan heater when running on the 2KW maximum setting. I'm guessing the additional 10 watts or so dissipated in the mains lead must have been considered as a "bonus source of additional heat" by the designers. :-)

Obviously, the oil heater section will draw the power selected by the power selector switch until the thermostat cuts out (assuming the stat was set for an achievable temperature).

[1] This thread has become rather disjointed in my news client (Pan) to the extent that I wasn't able to locate the OP to check the original question. However, it looks like he, as best as I can tell, was querying why the use of 5 similar type oil heaters were tripping out a 45A circuit breaker.

Since the heater elements have virtually a zero temperature coefficient of resistance, there's no issue of cold switch on surge loading to contend with so the only other variables are the chosen power settings and the effect of the thermostat switching the heating element(s) load on and off.

A gander at the rating plate should tell him all he needs to know (notably, the maximum power rating and the nominal voltage - typically since harmonisation, 230v). In some cases, the label may even show a second higher wattage rating for 240v. In any case, since the heating elements are a fixed resistance value, it's a fairly trivial task to calculate the 240v loading from the 230v figures if more precision is needed.

[John Rumm]

Quite allot of stuff specced for the UK market will quote the power assuming its running on the genuinely manly 240V rather than the nominal girly 230 euro volts.

So 2kW @ 240V suggests a load of about 29 ohms. So the actual power could be anything from 1608W to 2207W if you swing across the full permitted nominal 230V range of 216V to 253V

[John Rumm]

And maybe as much as 27A (for 2.5mm^2 T&E) depending on how its installed.

So unless you are right up one end of the ring, 36A would quite possibly never take either leg of the ring to max cable conductor temperature.

[John Rumm]

A ring circuit can supply many sockets over a floor area of up to

100m^2. So even if the individual load on a single plug does not exceed 13A, the total load on the circuit can be much greater.

Modern double sockets are nominally specced at 20A continuous load. Good quality ones will tolerate 26A of load for a reasonably period - although perhaps not continuously.

[T i m]

I'm guessing your 'obviously' above is assumed? ;-)

The OP could also have assumed that the power drawn would relate directly to the switch settings and the thermostat but it seems it does not.

Cheers, T i m

[T i m]

Oh the irony!

You are the chief poster of (especially) OT bollox here and I think the depth of said bollox is getting more and more desperate and bizarre. ;-(

Tip for you .... 'Do not open mouth until brain is in gear'.

Cheers, T i m

[Johnny B Good]

Indeed! As a matter of fact, I just spotted a response by ARW to this thread just after posting wherein he considerately quoted the attribution by Whiskey Dave who had posed the question as to why a test load of five such heaters had failed to trip the 32A circuit breaker on a lab bench supply of ,oddly, 220v.

To reiterate, WD had asked us to guess the actual wattage in spite of getting what I thought in the circumstance of the supply dropping from

220v down to a mere 202 volts (presumably with all five heaters plugged in - it would be extremely worrying indeed if this voltage drop was the result of just one heater), a rather accurate 1.6KW reading on his inexpensive Maplin energy consumption meter. A drop in power from the 2KW (presumed to be specified for a 230v supply) level down to 1.6KW on a 202v supply is exactly what one would expect.

Assuming a 1.6KW load at 202v, I calculate a heater resistance value of

25.5 ohms which neatly ties in with a 230v rating of 2KW. The amperage at 202 volts is a mere 7.92. For five such heaters, this represents a total loading of 39.6A which won't immediately trip a 32A circuit breaker.

As ARW succinctly pointed out, the problem would appear to be a wiring issue (compounded imo, by the strange choice of 220v rather than the more typical 240v of a UK mains supply). If the bench supply had stayed at the

220v level WD's test setup would have resulted in a current of 43.13A which may still not have tripped the breaker in a timely fashion.

Even assuming that the mention of a 220v supply was a typo for 230v, the current would have only increased to 45.1A on 230v, rising to 47A on a

240v supply. WD really needed to use 6 or 7 such heaters to test trip that 32A circuit breaker. TBH, I'm amazed that WD couldn't figure all of this out instead of making a fool of himself in this NG by asking such a foolish question to which he already had all the data he needed to provide the answer he sought.

[Andy Burns]

Maybe the college has been sold a system to regulate the site voltage down to 220V for "cost savings".

I know of an NHS estates dept that fell for that for a datacentre, and wouldn't hear a word of it when I said the UPS and SMPUs would merely take higher current (or the same current through more of the mains cycle) to make up for the lower voltage, and the aircon units would have to run for longer cycles, I suppose there would be a minor saving from the fluorescent lights being a bit dimmer ...

Or maybe another lab at the college got in first with their bank of oil heaters that took the supply down from 240V to 220V?

[pamela]

I think you take that throne. Johnny B Good's posts often contain a lot of sensible info.

[whisky-dave]

It seems to trip out at about 98C (halfway up the last fin) so drops to 700W at that point.

That seems to be what is happening.

Seems to drop to about 76C then then the full power comes on 1725W.

Seems likes what's happening, but if I were designing a cut-out to stop ov er heating I'd get the whole thing to switch off to 0W as a safety feature. I thought that's what all cut-outs did.

taking their new stuff apart and I don't particually want to.

What plastic end cover ?

t then that one was over £100 rather than £35.

I think it does as it does with almost anything else and my home one is 2.5 KW.

[whisky-dave]

How ? Surely it's just basic ohms law, 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.

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

[whisky-dave]

That seems to be true with bathroom down heaters but not with others.

[whisky-dave]

As I've posted previously.

220-240V 50Hz 2000W. So does that mean it doesn't matter whether the voltage is 220 or 240 it'll always use 2000W not 1999 or 2001 exactly 2000.

Seems you expect rather a lot of tech info from a stick on label.

[whisky-dave]

Why oddly at 220V I don't think I've seen it much higher.

Yes all on ONE phase from ONE MCB breaker.

That's about it.

Yes this is what we found we didn't expect immidiate unless all heaters wer e switched on at the same time,it was a trial to see what would happen if s omeone strted up everything at the same time, but it was over 2 hours befor e it tripped out.

Well the idea was that we didn't want the power tripping during a lab or le cture so tried running worse case senerio with what we had to hand.

which it wasn't my office with ONE heater at 700W , 212V dropping to 211 w hen the heater switches to 1.7KW.

I didn;t have 6-7 heaters at the time just 5 .

That wans't my original question that is why, and you've avioded the origin al Q.

If yuo have a 2KW heater switched to full on what is it;s power consumption adn of course you''ve got that wrong it's NOT 2KW not 1.6KW not even 1.4KW not even 1KW but 700W .

SO like opur so calledheating engineers must have done hopw many 2KW heater s does it take to raise the temperature from 14C to 16C.

How dos that change is the 2KW heaters donlt give out 2KW but only 700W how does that change teh calculation.

Now the original heating system was put in in the 50s , the engineers told the college that they system wasn't designed for such a long run through 2-

3 departments i;e the heating conduit path was too long to maintaine the te mperture. This is why the lectures offices get really hot so they academic s open their doors and windows and by the time the heating conduit gets int o the lab the air is almost cold if not colder than the outside temperature .

All we need is a heating engineer that knows stuff, both theory and in prac tice It was 12C @ 9am, now 16C @ 13:45.

This is with 5 of 2KW heaters and 2 of 1.5KW heaters.

So if yuo wanted the demp to be 16C before the 10am class how many heaters would we need in total. ?

[T i m]

Right, it sounds to me like there is a 100 DegC upper limit stat and only the heavy heater element is going though it.

Ok.

Yup, sounds about the right hysteresis range for a thermal limit switch.

Quite.

You would think ... however, it may be that the actual switch they use can't handle the extra 700W or it was considered that the 700W element couldn't get the rad into an overtemp condition or it was just badly designed or incorrectly wired.

Normally the controls / wiring are in a plastic cover of some sort (so you don't burn yourself when touching it and it's cheaper to make etc).

I'm saying 'it shouldn't'. It may be that this entire batch of heaters have been designed badly or wired incorrectly ... or that there is a second upper-limit stat (or more likely a thermal fuse) that would ultimately protect the rad from a real overtemp situation (like if you covered it in towels, even when only on the 700W element).

Cheers, T i m

[whisky-dave]

So it's not realy a cut-out more like a cut-back.

So what does a cut-out do.

So is that the new name for a cut-out.

over heating I'd get the whole thing to switch off to 0W as a safety featu re.

But of course it's not called a cut out but Overheat protection.

So many options to consider one wonders how yuo;d calculate how many heater s would be needed, it;s a problem we're having at this very moment and disc ussing , how many more to buy and who should pay for them.

thought the plastic would be likely to melt and if I did it would then fail regualtaions as we;d need it PAT tested before it was put back into use. So another reason njot to take it apart, I'd prefer that we were supplied with working equipment that was up for the job.

but then that one was over £100 rather than £35.

Well it does just like anything else, or at least you should expect it to.

Nothing of which help work out how many we need. Perhaps that's why we have 14 due to arrive this week.

[John Rumm]

It seems like working out the heat loss from first principles would be a good start:

Once you have a feel for that, you know what power input you will need to maintain a steady state at a desired temperature. You would then need to size the heating to be able to exceed that by enough to lift it to a working temperature in a reasonable time frame (and what that is will depend a bit on how the place s built - you may be able to achieve it in a few hours, or you might need to heat it continuously if it turns out the answer is "days").