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#177409 - 05/01/08 10:29 PM What constitutes a Tungsten load?  
BigB  Offline
Joined: Mar 2004
Posts: 719
Tucson, AZ USA
A particular timer lists it's various ratings. It says it can handle a resistive load of 1,800 watts, but only 1,000 watts of a tungsten load. I thought incandescent lamp filaments were made of tungsten. Does this mean it can handle an 1,800 watt wall heater, but only 1,000 watts of incandescent lighting?

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#177411 - 05/01/08 10:53 PM Re: What constitutes a Tungsten load? [Re: BigB]  
renosteinke  Offline
Cat Servant
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
They're referring to HID lighting ... the ballasted Mercury, HPS, and MH types.

#177412 - 05/01/08 11:12 PM Re: What constitutes a Tungsten load? [Re: BigB]  
twh  Offline
Joined: Mar 2004
Posts: 916
Regina, Sask.
Originally Posted by BigB
Does this mean it can handle an 1,800 watt wall heater, but only 1,000 watts of incandescent lighting?

I think so because I'm pretty sure that in Canada switches on incandescent lights need a tungsten rating for a similar reason. Or, at least they did at one time. The explanation was that tungsten has a higher current draw until it heats.

#177415 - 05/02/08 04:02 AM Re: What constitutes a Tungsten load? [Re: twh]  
Trumpy  Offline

Joined: Jul 2002
Posts: 8,217
SI,New Zealand
This sounds a tad strange,
Are you sure you aren't getting the inductive rating of the contacts of the the timer, mixed up with an incandescent rating?
Inductive circuits need higher rated contacts, because of the in-rush current and breaking current, or de-rating needs to take place.

Just my $0,02 worth. smile

Let's face it, these days if you're not young, you're old - Red Green grin

#177418 - 05/02/08 07:53 AM Re: What constitutes a Tungsten load? [Re: Trumpy]  
homer  Offline
Joined: Sep 2004
Posts: 68
Vancouver, WA, USA
Yes, tungsten is the rating for incandescent filament loads. The amperage draw for these lamps is much higher when cold than after heating up, although it is somewhat instantaneous. Throw an amprobe on a bulb and use the max setting on the amprobe. You'll see quite a difference.

#177451 - 05/03/08 04:30 AM Re: What constitutes a Tungsten load? [Re: homer]  
RODALCO  Offline
Joined: Dec 2005
Posts: 854
Titirangi, Akld, New Zealand
It is a correct statement on the time clock!

A tungsten load has a lot higher inrush current, cold about 10 times more then hot.

For example a 100 Watt, 230 Volts lamp has a very low resistance when cold. (42.9 ohms) Just measured with a calibrated ohm meter.
When the filament is hot the resistance increases considerably. (about 529 ohms.)

A resistive load, like heater elements, don't change much in resistance value between cold and warm.
From memory the 3 kW 230V hotwater element is about 17 ohms (cold) It may increase to 19 ohms when hot.

It explains also why most lamp filaments fail at switch on, because of the large initial current flow which shakes the cold filament apart + the thermall stress shock on top of that as well.

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