Electrical Heat Trace Circuit Breaker Choice 3

[JohnnyHS]

Good Morning All!

you guys are usually so helpful so i'd thought i'd put this little poser for you electricals to lap up. Am sure this is bread and butter for y'all but for a mechanical process guy its made me think twice as well as a few guys around here and i would like to consult your learned opinions...

OK. I have an electrical heat trace (RAYCHEM self regulating @ 120oC) application which has a current draw of 6.7A.

The question.

What breaker shall i use on this application. I have consulted the manufacturer who says a 10A "Type C" Breaker but various other sources including a few electricals have said oh no definitely use an Earth leakage circuit breaker instead.

What would you use? I want to justify it in my own mind rather than go "oh the manufacturer says that so i will" or "The greybeard electricals said that so i will" I am pretty sure both will do "the job" for what they are intended for but your opinions are most welcome for either option (or a fresh one if you have one!!)

Thanks


Johnny H-S BSc(Hons) MInstMC

Engineers like to solve problems. If there are no problems handily available, they will create their own problems.

 

[waross]

The answer may depend to some extent on the type of control panel and where in the world you are.
Different countries have different codes, and some control panels have a lot of sophisticated capabilities.
Don't forget that self regulating traces may have a much higher current draw when cold.

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

 

[rbulsara]

Earth leakage sensing type CB will provide additional protection against shock hazards but it may or may not be required by code where you are.

Following manufacturer's "published" recommendation is also important.

Rafiq Bulsara

http://www.srengineersct.com

 

[JohnnyHS]

ok thanks for the replies guys.

bit more information.

1) The system is going into a Romanian Refinery. The specifications as to what is acceptable is very vague from the client but we are under obligations to supply a functioning safe system under our (UK) specifications (statute and good practice, IEE regs etc)which would be compatible with another EU "friend"

2) The Control panel i am speccing at the moment hence the "what type of breaker for the heat trace" question. i will give this information out to the distribution board manufacturer.

If the ELCB is additional protection I am leaning to a ELCB rated at 10A. cant go wrong for being too safe eh! I take it the ELCB and a CB Type C will break when a fault condition arises but the ELCB is quicker??

Johnny H-S BSc(Hons) MInstMC

Engineers like to solve problems. If there are no problems handily available, they will create their own problems.

 

[Kiribanda]

JohnnyHs,

10 A circuit breaker having Type C tripping curve (IEC 60898)is suitable for your application.It will provide adequate overcurrent protection for each heat tracing feeder.You may use a 2.5 sq. mm cable.

In addition to the above overcurrent protection you should provide earth leakage protection (I presume that your LV network is having TT earthing method per IEE Regulations/IEC 60534)for all heat tracing feeders.The reason being that an uninterrupted power supply for heat tracing (for certian refinery products like sulphur)is very critical.Its main objective is not human protection.There is always a great possibility for the tiny heat tracing elements wrapped around metal pipes loose their insulation and create earth faults.Therfore, 300 mA (used for lighting circuits)earth leakage circuit breaker should accompany the 10 A circuit breaker mentioned above.

 

[rcw retired EE]

Check the cold start current against the trip curve. As others have noted, the self-limiting cable draws a lot of current when it is turned on in cold weather. The supplier's software usually provides a recommendation for the minimium rating of a circuit breaker on a given circuit.

Sometimes the information is given as the maximum length of each type of heating cable that can be placed on a 20 Amp or 30 Amp circuit.

 

[JohnnyHS]

Kiribanda,

Thanks for your help. in particular you have opened my eyes to the actual function of the ELCB. I thought that it did the overload protection AND earth leakage. I was wrong and your last post made me investigate further..

Fellow Viewers,

http://www.the50plus.co.uk/tech_support/RCD-ELCB-RCCB explained.htm

This link is very good at explaining the difference and similarities of the components covered (and not but relevant) in this subject.

With regard to my application I believe i need a RCBO which will protect against earth fault (for safety) AND overload currents (i do not need a fully constant heat trace supply so this overload current protection is fine and compliant with good practice).

I will specify this in my specification now. Thanks for your help everyone

AH HA! - Two things though,

Firstly

Kiribanda, you suggest 300mA. This is pretty high is it not for a shock if a person was to become exposed to the current? i was thinking 30mA?

http://hypertextbook.com/facts/2000/JackHsu.shtml

OUCH! :-(

Secondly

does anyone know the symbol for it! lol i think i'll just use an isolator switch symbol and text surround it with a description unless one of you good people can show me the light

Johnny H-S BSc(Hons) MInstMC

Engineers like to solve problems. If there are no problems handily available, they will create their own problems.

 

[JohnnyHS]

BINGO! (and who doesnt love BINGO!)

http://www.toolstation.com/shop/Ele...on/GE+RCBO+10A+30mA+Type+C/d190/sd2615/p17137

http://www.hbo.com/larrydavid/episode/season5/episode44.html

Johnny H-S BSc(Hons) MInstMC

Engineers like to solve problems. If there are no problems handily available, they will create their own problems.

 

[Kiribanda]

JohnnyHS,

30 mA is the threshold level for all domestic circuits where people are using electricity.For swimming pools it is 10 mA which is obvious.But circuits like street lighting etc where normal unskilled people are not touching every time,but maintained by skilled qualified personal,then 300 mA is a reasonable threashold level.Also 30 mA is such a low value that it might give nuisance tripping even for a little leakage of those tiny electrical heating elements.Therefore, 300 mA seems to be a reasonable value for your industrial setup.

The manufacturer of heating elements will give you the appropriate mA value to set.

 

[davidbeach]

It all depends on where you are. In North America, GFCIs for personnel protection are 5mA, 30mA is only suitable for equipment protection, such as heat tracing.