Heat Trace Start Up current

[rrzzan]

Hi Guys,

Can anyone provide me the formula for calculating the 'start up' current for heat tracing?

If I have normal heater operating amps 18.5 A, How would I determine the 'start up' current?

Thanks.

 

[davidbeach]

What does the manufacturer's literature have to say?

 

[rrzzan]

It does not say about sizing a breaker.

All I know is the CB should be sized based on ambient temperature (which is -20) in my case. This is based on the fact that the heater will draw more current as the temperature drops.

 

[itsmoked]

The maximum current then would be the lowest temperature. This is likely what the tape is rated at. Your 18.5A will be the maximum. Choose a breaker accordingly.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[rrzzan]

Itsmoked,

Let me put it this way. The normal operating current(at ambient temperature) is 18.5Amps.

But if the heater is to START at -20 degree centrigrade, the heater would require more current then the normal current. I would like to know that 'starting current'. Any factors or formule for this?

 

[itsmoked]

Sorry no! The tape should be limited to some amount that is stated on it or on it's literature. How would an electrician install it if on a really cold day it tripped breakers.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ykee]

Heat trace manufacturers provide a length/breaker size limitation. Usually power consumption is listed in terms of length of cable, ie: 6W/ft, and may have a different value if it is dry air or if it is in snow and ice.

Are you trying to figure out operating cost, or are you trying to size breakers?

 

[waross]

Self limiting?
Mineral insulated?
Straight resistive?
Start up current of heat trace is all over the map, depending on the expected ambient and the type of heat trace.
You need to find the manufacture's literature. Google often helps.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rrzzan]

I'm not gettting it. The length is fixed based on supply voltage and and the Circuit Breaker size. I don't have any problem with that.

I'm using self regulating cables but it really doesn't matter much what kind of cable you are using to determine the circuit breaker size. The method for determining the 'start up' current should be the same if you know the normal operating current and the lowest ambient temperature.

Ykee, I'm trying to size the breaker, which should be based on the start up current. And the start up current is based on the lowest ambient temperature which is negative 20 centigrade in my case.

 

[davidbeach]

Resistance of the cable at -20C is very different than the resistance of the cable operating in a -20C ambient. Different cables have different properties. The manufacturer can provide the information you need. No formula that applies generally, you have to know the properties of the cable.

 

[rbulsara]

Besides any amount of so called start up current (not sure what it is) will not trip a thermal magnetic breaker just on "start up".

Even say it is 3 times the rated current, if you select a 30A CB (based on 18.4A), the breaker will not trip on 60A for several seconds. After all heater is not a motor.

Any breaker sized for 1.25% of the rated current or one size larger (of you are in doubt) would suffice. For higher rated breaker you need to select the conductors accordingly.

For anything more definitive you need to consult the mfr. as advised before.

 

[waross]

You obviously haven't spent any time in a warehouse checking the availability of a particular heat trace spec. Try 3 or 4 different combinations of heat density and operating temperature. They look the same except for one or two characters in the type number. What is the formula??
GOOGLE THE MANUFACTURER'S SITE.
In some installations the trace is strapped to a large heat sink. that is a large, cold steel pipe full of cold product. The heater may take enough time to come up to temperature that the breaker may have to withstand "cold current" for some time.
Check the spec's!!

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[roydm]

I once had to trace a long line carrying Bunker C. At startup the breakers tripped a couple of times but once the internal temperature rose a little it never tripped again. Surely the vendor can give you the expected current draw at lower temperature.