GFCI Breaker Question

[RBM]

The original question was real simple and straight forward. The word watt or wattage was never introduced, except by you

[DerbyDad03]

Once again - and I'll be real specific this time - tell me how *watts* has anything to do with the question I asked in this thread?

Why don't you copy and paste the part of my question that requires an explanation of power in your next response so we can all see what you are talking about.

[clare]

The only one I saw was a combination GFCI/AFI and had LED trip indicator that showed if it was a GFI or AFI trip. No indicator meant over-current. Cannot remember the brand off-hand.

[clare]

LOTS of them, particularly AFI, ARE microprocessor based.

[clare]

If it is a thermal breaker it responds to wattage. If it is magnetic it responds strictly to current. Many are combination trip.

[gfretwell]

Siemens/Murray

[David Nebenzahl]

On 1/18/2011 2:23 PM DerbyDad03 spake thus:

"Over-current" is absolutely the correct term here. Amps, dontcha know.

[clare]

Sounds right.

[Ralph Mowery]

There was a similar question a day or so befor this one. When similar threads start, it is easy to get confused as to which is which, especially when they get long. The heading was can "wattage" trip a GFIC or something similar to that. The Wattage was in quotes as maybe the poster did not use the correct term of current, although it really was a wattage question the way it was put.

Here is part of the question:

"I believe that it's the pure wattage requirements of these lights, more than their quality (or lack thereof) that caused my GFCI to trip."

Does that make any sense?

If it was an current overage the breaker would trip not the GFCI so why would a "high wattage" device trip the GFCI?

[DD_BobK]

Some of the people reading it, don't read so good?

[David Nebenzahl]

On 1/18/2011 5:03 PM [e-mail] spake thus:

AFCIs might have some digital brains in 'em, but so far as I know GFCIs are purely analog devices (basically a current comparator). And electromechanical to boot (that's what pops the little button out).

[RBM]

That is not a "GFCI" circuit breaker. The OP question was regarding a GFCI breaker. A combination AFCI/GFCI is not used for class A ground fault protection. There is no GFCI breaker, new or old, that has an indicator to determine the cause of the trip

[bud--]

All the breaker knows about is the current going through it. Both thermal and magnetic elements trip on current. Thermal gives you a time delay inversely proportional to current (which is where the early brand ITE - inverse time element - came from). Breakers in your house are thermal (time delay) and magnetic (instantaneous).

[clare]

Not 100% true. Thermal breakers take less current to trip when the voltage goes up, and more when voltage drops, so are "power sensitive" instead of "current sensitive".

Magnetic breakers operate on "ampere turns" - the coil has X number of turns of wire on it, and a portion (depending on the design) of the load current goes through that coil. When the current through the coil gets high enough the breaker trips. A 600 volt 20 amp magnetic breaker will trip reliably on a 24 volt system as well as on 600.

A 120 volt thermal breaker will trip at a lower current on 240 volts, and will require an extremely high current to trip on 24 volts.

Most American residential breakers, being "hybrids" work well on 120 volt circuits but would be useless on say a british 240 volt system. Not totally useless, because the instantaneous magnetic trip would be fine, but the thermal would trip too fast.

[Ralph Mowery]

Both magnetic and thermal breakers only operate on current. It does not mater what voltage is being used. You are fine on the magnetic, but wrong on the thermal breakers.

A magnetic breaker operates almost instantly on an overload. The thermal breakers (almost the same as fuses) will operate on lower voltages than the maximum ratings just fine. They have a small amount of resistance material in them that heat up depending only on the current. I just looked at a single breaker that is normally used in houses. It is rated at 20 amps and states it is for 120/240 volts. The thermal breakers are sort of time delayed. They take time to trip depending on how much over current is put through them. If say a 20 amp rated breaker has 22 amps going through it, it may take 30 minuets to trip. If it has 25 amps, it may trip in 1 minuets. If it has 40 amps , it may trip in less than a second. The exact trip curve will depend on the breaker.

[clare]

Well, my experience using a heavy duty thermal/magnetic breaker on a low voltage DC application flys in the face of your knowledge. The breaker in question has an adjustable magnetic (fast) trip and a fixed thermal(slow) trip. On 24 and 48 volts 450 amps would not trip the thermal trip in 2 minutes. I could adjust the magnetic to trip at any current I wanted, from about 50 amps up - and it tripped very reliably at that current on both 24 and 48 volts (DC). On 120 volts 80 amps would trip the thermal in less than a minute. This was a 3 phase breaker designed for use on a standard commercial 3 phase system (115/208/whatever) and was used in an electric car as the main circuit protection.

[bud--]

I have no idea what breaker you are talking about and you don't say. If it is a commercial unit it well may have a CT (current transformer) in the sensing circuit for current. CTs are useless for DC. 3-phase breakers are not rated for DC. You were using the breaker for a use it was not intended and you don't know how it works.

And it tripped on 120x80 = 9600W AC in "less than a minute". It did not trip on 48x450 = 21,600W DC in 2 minutes. How can you say this breaker trips on watts?

"American residential breakers" (from your previous post) have a thermal element in series with the contacts. In one variety of breaker, which gfretwell has provided a nice picture of in this thread, the thermal element is the "O/C device", which is plainly series connected. If it is series connected it responds to current only. It is a bimetal strip that is heated by the current. It is the same type of thermal element that is series connected in "American residential breakers". It responds to current, not power.

But who knows what happens north of the border.