ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals

Topic Options
Rate This Topic
#177409 - 05/01/08 07:29 PM What constitutes a Tungsten load?
BigB Offline
Member
Registered: 03/31/04
Posts: 719
Loc: 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?
Top
Work Gear for Electricians and the Trades
#177411 - 05/01/08 07:53 PM Re: What constitutes a Tungsten load? [Re: BigB]
renosteinke Offline
Cat Servant
Member
Registered: 01/22/05
Posts: 5316
Loc: Blue Collar Country
They're referring to HID lighting ... the ballasted Mercury, HPS, and MH types.
Top
#177412 - 05/01/08 08:12 PM Re: What constitutes a Tungsten load? [Re: BigB]
twh Offline
Member
Registered: 03/11/04
Posts: 901
Loc: 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.
Top
#177415 - 05/02/08 01:02 AM Re: What constitutes a Tungsten load? [Re: twh]
Trumpy Offline


Member
Registered: 07/05/02
Posts: 8211
Loc: 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
Top
#177418 - 05/02/08 04:53 AM Re: What constitutes a Tungsten load? [Re: Trumpy]
homer Offline
Member
Registered: 09/30/04
Posts: 68
Loc: Vancouver, WA, USA
BigB,
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.
Top
#177451 - 05/03/08 01:30 AM Re: What constitutes a Tungsten load? [Re: homer]
RODALCO Offline
Member
Registered: 12/08/05
Posts: 854
Loc: 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.


_________________________
The product of rotation, excitation and flux produces electricty.
Top

Member Spotlight
Member Since: 05/03/03
Posts: 1137
New in the Gallery:
SE cable question
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box


Who's Online
0 registered (), 93 Guests and 9 Spiders online.
Key: Admin, Global Mod, Mod
 
New in the Gallery:
SE cable question
 
Top Posters (30 Days)
Admin 47
HotLine1 43
gfretwell 19
Ruben Rocha 12
Trumpy 9
 
Newest Members
KrmtFrg, Stack, Scotto, Freecrowder, clee512

ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals