ECN Forum Forums General Topics of the Trade General Discussion Area What would you expect?

A 20A 2 pole breaker has a load of 40 Amps line to ground on one side only. What amount of time should the breaker trip at twice it's rated load?

Several seconds is expected to reduce nuisance tripping on motor-start-up loads, but what would be considered extreme on the high end?

How fast would a 20A fuse blow under 40 Amps?

A time delay 20A fuse under 40 Amps?

At what percentage should a breaker trip within one minute? 120%? 150%? 200%?

Is there any info out there that may give me the data of what UL expects from a breaker or fuse?

Sparky,
You need to find the time-current curve for the device that you are using. The only one that I could find this morning for a 15 amp FRN-R fuse. It shows that this fuse will hold on average for 90 seconds at 20 amps, 30 seconds at 30 amps, and 2 seconds at 60 amps.
Other fuses and breakers will have different curves.
Don(resqcapt19)

I guess what I'm after are time current curves for:

FPE 2 pole 20 A
FPE 1 Pole 20 A (If it differs)
GE 2 Pole 20 A
SQD 2 Pole 20 A

If the hard data already exists, it will save me a lot of time. I've got the data from my own experiments, but I have a rather "noisy" lab.

I'll let you guys know what I found out, but I want to know your opinions (and any hard data you may know of) first.

You may be surprised!

[This message has been edited by sparky66wv (edited 02-13-2001).]

I looked at a curve for a SQ D 2 pole 50 & it shows a one minute trip at about 130%.

As Don pointed out, each breaker by each manufacturer will have it's own trip curve. You could probably contact UL to find out what they expect, but they would probably have to sell you the standard & they're usually expensive.

In a nutshell... here are the results of my, uh..."tests"...

Single Pole 20A Breakers FPE on a 40A load to ground tripped between 38 and 74 seconds.

Double pole 20A Breakers FPE on a 40A load to ground tripped between 45 seconds and well over one minute (90+ sec). One breaker failed to trip after two minutes at 200% load. The 30 Amp SQ D Breaker upstream tripped instead, within 2 minutes at 150% load.

A SQ D 20A Breaker 2 Pole tripped within 20 seconds at 40A.

The 20 Amp breakers were the only ones I could test "safely". I had no idea it would take 200% to trip them in less than a couple of minutes. You should have seen me trying to find every high current device in the house to get these things to trip. Toasters, Coffee Pots, Blow Dryers, Heat Guns, Shop Vacs, etc. etc. Scared the cats...

I had it on two GFCI 20A receptacles. But even the #12 feeding them didn't get terribly warm, at double their "rated" current.

By the way, my wife is a nurse and is here when I do these crazy things... Wait 'til I get my Tesla Coil up and running!

'66

I'd like to be the first to congradulate you on getting any FPE breaker to trip under any condition. I've met quite a few electricians who feel that an FPE breaker that trips out is in the realm of an urban legend.

[This message has been edited by Tom (edited 02-23-2001).]

'66

You must be in the Smoky Mountains?


(Joke)

Bill

I've cut live wires in two during remodels( by accident of course )frying my Kleins only to have a 20 Amp stab-lok breaker laugh in my face.

Look here for more! www.stargroup.com

[This message has been edited by Joe Tedesco (edited 10-06-2001).]

www.joetedesco.com

[This message has been edited by Joe Tedesco (edited 04-26-2003).]