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

[John Rumm]

its can be general purpose and have high integrity earthing - the two are not exclusive.

Lots of places use mains filters of various types for IT kit. They are (mostly) useless to be fair.

If you want proper protection for IT stuff, then either a line interactive or online UPS is the way to go.

Well its very relevant to the conversation we have been having and to some of the questions you asked. It may not be your responsibility to know about these things as a part of the job, but that does not mean you have to pretend to be ignorant of the actual details.

Those are flexes not cables. The cables form part of the fixed wiring between the CU and sockets etc.

Flexes are far more vulnerable to L to N faults than cables, but do have the advantage of dedicated fault protection from the plug fuse.

If you look at that photo of your CU, all the "Ring room nnn" circuits are general purpose circuits. The ones labelled things like "Door spur", "door bell", "security panel" etc are not general purpose circuits.

(Note that general purpose has specific meaning in this context)

Indeed you would expect a drop, but the amount you got was rather large.

A typical bit of kit to suffer would be something with a compressor driven by an induction motor. Some fridges / freezers can be quite sensitive, either having insufficient torque to start and stalling, or drawing too much current and overheating.

Well that's ok then... for you.

Yup.

We can do an adiabatic check to be sure:

S = sqrt( 60^2 x 0.1 ) / 115 = 0.16 mm^2

Since the smallest lighting cable used is 1mm^2 (and 1.5mm^2 being common in larger installations), you would have loads of headroom.

The existing wiring as far as the fittings would be fine. With some replacement tubes you would need to alter the wiring in the lamp fitting to wire the ballast out of circuit.

(Although you can get some "straight replacement" LED retrofit tubes that will work with the ballast)

[whisky-dave]

Well as long as someone else knows when and when not to install high integr ity earthing, I've no idea.

Are yuo sugegsting managment could be fooled by the company installing thei r prodicts ;-)

But what if you have a mix of uses in a lab. This isn't an IT lab, we have aa whole 3 floor building for that.

There are NO problems that I can see. Whatever happened to trip the MCB, now if the MCB hadn't tripped would that have been a problem ?

We call them cables not flexes.

Our students don't get access to them as they are in conduit. Students don't get access to them.

So the only flat cables our students ever see are IDC ribbon cables, for th em that is what a flat cable is.

Strangly enough none of those are in use, haven't been for years.

Well that woukd depend on the 'Zero' no load point wouldn't it I mean if th e voltage off load starts at 223V rather than 240 or even 230......

Interesting you should ay that as on friday or CNC machine cut out, this ha s a densist grade compressor attacheted to it adn because the room was cold a heater too room 252. Today no ones in their it's cold nothing is on and the mains voltage measure 216V .

So that could be whats been going wrong.

Yep, as I've said and the previous managers have saiud the heating in the l ab or department hasblt worked in 35+ years why don't you fix it.

I wonder why they don't give similar headroom for general purpose mains.

We replaced 4 tubes will LED versions without rewiring they seem to work fi ne.

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[Martin Brown]

You need to do the test with two different total power levels to determine unambiguously what the thermal capacity and other losses are.

The simplest way out would be to use a couple of 2kW air curtain heaters over the lab doors which will rapidly warm the *air* inside the lab to a comfortable temperature instead of these useless convection heaters heating up the wall behind them and air that immediately rises up to the ceiling. The room fills with warm air slowly from the top down.

Any kind of fan heater would be way better than oil filled radiators if you want to get the room habitable in the shortest possible time.

Those propane powered fan flame things for heating big garage spaces are pretty good and fast if you don't mind the smell of combustion products. (I find them a bit scary YMMV)

[T i m]

John gave him all the help for calculating the room losses but I'm pretty sure it was more than he could be bothered with (and would rather bite the hand that feeds him here in the big gaps between leaning the labs between classes that do that).

He has said fan heaters are not allowed (as it might melt the snowflakes) but I'm not sure if an air curtain (that I think I also suggested) would count as such.

But if they have low ceilings and people moving about?

They do but can't (not allowed).

If fan / convectors heaters aren't allowed ... !

I would still be interested to hear the outcome of the test of leaving

*just* the 1300W element on, to see how long it takes before it overtemps (if it does at all).

Also, given the 700W element doesn't appear to be protected by the (same?) overtemp stat, it's possible the rad would cool faster if it went from 1300W to zero, rather than 2000W to 700. This might get the heating back on quicker as it's likely the 700W element would slow the time the heater took to get back down to the point where the overtemp stat cut back out (in electrically) again (stat hysteresis).

Then I wondered if the alternative 1500W heaters might not overtemp on full, but noticed they have a smaller surface area (7 as opposed to 9 'fins') and so it would probably be the same issue with them being 'overpowered'.

I've ordered a couple of electronic power controllers to experiment with my own rads [1]. The aim is to limit the power to that that they can actually dissipate as they are only going to be used to provide 'background' heating in the bedroom and I'd rather not hear either of the stats clicking in and out all night. ;-)

Cheers, T i m

[1] And any heat the controllers dissipate will only go into the room in any case. ;-)

[Martin Brown]

Some much for engineering education in the UK. :(

It would be by far the simplest solution for a largish laboratory a bit noisy when heating things up from cold but once the air is warm a relatively modest heat input from radiators can hold it there (especially once the room is occupied by a decent number of people).

Our village hall has essentially the same problem of wanting to get it to working temperature in the shortest time with the least energy usage and only having electric heating available.

Unless they are walking round on the ceiling their feet will freeze.

OK then a cold fan pointed at the useless convection heater(s). Strange that an organisation that prohibits fan heaters permits overloading of the lab ring main without a second thought.

Chances are that upping the power for some of the time will always result in more heat output overall. The problem is that they are losing heat too fast and heating up the wrong things mostly the air against the ceiling and walls behind the oil filled radiators. Some fans on the ceiling to push the warm air down would help a bit.

If you don't mind being dirty about it you could do what the electric blanket people do with a diode in the supply to halve output on low.

[T i m]

;-)

Quite.

I guess that depends on the duty cycle. 2000W with a 50:50 duty cycle won't be as affective as 1750W for 100%?

Agreed.

I had considered that previously and even putting two heaters in the room with each on one / different half cycle. ;-)

Cheers, T i m

[Martin Brown]

I am thinking of doing it to my office cooling fan but it wasn't warm enough this summer. It has settings called low, medium and high.

Even on "low" it moves sheets of paper off my desk several metres away. The settings are more accurately gale, strong gale and hurricane.

[T i m]

Cheers, T i m