PapWiel

I’m no electrician, but I do know a thing or two about electricity

I’m from South Africa, where we are currently experiencing a major power (electricity) shortage. The whole country is under a load-shedding schedule where regions are switched off from the grid from 2-4 hours at a time, and then from once a week to daily.

I’ve noticed in Johannesburg that many of the big corporate buildings leave their florescent lights on during the night (when all is suppose to be sleeping.) I’ve heard the story that it consumes more power switching a whole buildings light on, than it is to run it continuously. Surely that’s a load of Bull?

Is there perhaps a sparky on the forum that can shed more light on this “Myth” or shall I get “Myth busters” to clarify this one? 

On the same subject. What about 1kw single phase motors? It’s also rumored that they should be left running for 8 hours rather than starting them every 30 minutes and leave it running for 5 minutes. We’ve always been told that in order to save power, you won’t keep a kettle running, you’d rather just switch it on as required.

dknguyen

??? Only when you're switching continuously. I don't see how switching once per night would consume more power than just leaving them running the entire night. And don't fluorescent controllers switch anyways when they're running? I think they just might be leaving the lights on to deter burgulars like they do here.

SAme thing goes for the motors? It doesn't seem the switching is having frequently enough to consume more power than continuously running. However, sometimes motors are run doing nothing to offset the powerfactor used by all the induction motors in the factory (which themselves heavily skew the power factor one way).

It might be that it is harder on the motor to start and stop it like that than just leave it running. I don't think it would consume less power.

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ericgibbs

hi Pap,
The myth busters did actually blow this myth about leaving lights ON.

They found it saves money if they are switched OFF when not in use, the same logic applies to 1KW motors on that 30min cycle, turn it OFF.

You have only two more years of Eskom cuts!...

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PapWiel

Thanks Eric.

BUT, as far as Eskom and the blackouts go, we still have 5 year before the first of the three new COAL fired power station will be in commission. Madupe, the first to go up is only planned to be productive by 2013. I don't know where the power will come from for the 2010 Soccer world cup. All you people from the rest of the world planning to visit for that event, remember to bring along a flashlight

ericgibbs

hi,
I bought candles in PE this year, it looks as though the new PE sports stadium is on the back burner.. budget problems.

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zevon8

Likey not your case, but in colder climates the lighting and office equipment, and very much the staff, provide alot of the heating in a large building. Lights are left on at night to help hold the temperature.

Many pieces of office equipment will give a BTU rating to show the heat production they produce.

dknguyen

I thought they left the lights on so you could see burgualrs getting in.

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rjvh

wouldn't trust that to hard

that's what they said here in cambodia also but still i have 5 times a week power cuts of more that 6 hours

3 years aggo it whas next year it's over we building new plants already
new plants where there but where calculated ont the demand during the calculations so no extra capacity antisipated

2 years aggo same story but with the aditional message that cambodia would be conected to the regional grid network (vietnam)

1 year aggo still no working power line athougt it is build, with the message of the power line all future planed power plants came to a hold and nobody did build annything annymore because of the prommised cable from vietnam

what do we see now vietnam is also booming same as cambodia and gues what they have also power cuts now and don't even sell power to cambodia
i believe the line will be working end of this year but if that is the end of the powercuts i know for sure it's not

Robert-Jan

RODALCO

The fluorescent story is a nonsense.

Put an analogue ammeter in series and see the currentflow during the startup cycle. It may be double or three times the running current when the starter is closing it's contacts to strike the arc in the tube.
When the lamp has striken, the current remains steady and reduces even a little when the lamp warms up.

If the light is not required within the next 5 minutes or so just switch it off.

With motors you have to look at the duty cycle. For light starting loads just turn it off when not needed.
For high inertia loads e.g. compressors, heavy flywheels etc. The motor manufacturer will specify how many starts the motor is allowed to do over a one hour period without overheating the windings.
Other matters to bear in mind is wear and tear on the starting contacts.

If a machine is well designed these should be adequately rated.

My $0.02 worth on this subject.

Regards, Raymond

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Hero999

zevon8,
That doesn't make any sense because most places are heated by natural gas, oil, coal or even wood which is much cheaper and efficient than electricity.

rjvh,
I'm not having a go, (English probably isn't your first language and you might never know if no one tells you) but there's only one g in ago not two.

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rjvh

Hi hero 999
i am totaly not offended by your coment and i do apriciate if people correct me

english is not my first language and on top of that i am also dislexic

that means that i write as that i remember it and other wise as how you say it

spelling checks realy works fine for me before i send a letter out but i still didn't get the spelling check working in this sites reply box's

Robert-Jan

Hero999

What broser do you use? Firefox and Opera have a spell check function built-in and spell check plug-ins can be found for Internet Explorer.

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zevon8

Lighting and people are very much factored into the heat load of a building. Lighting alone can account for up to 30% of the heat load in a typical office, people factor up to about 20%. When sizing HVAC systems these numbers are significant.

One calculation for heat load:
http://www.engineeringtoolbox.com/he...hts-d_709.html

A major study to help designers and engineers:
http://www.ashrae.org/pressroom/detail/13367

Brief description of HVAC sizing based on flourescent or incandescent. ( note they mention eliminating heating based on lighting )
http://tristate.apogee.net/cool/cfrl.asp

HiTech

Especially in residential settings, lights are an "on demand" type of energy source. Only use them when necessary and save money by keeping them off when not needed.

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mneary

I have a PIR in my workshop. Saved me a fortune when I installed it. It even turns the soldering iron off if I've forgotten it.