How to test current rating of Miniature Circuit Breaker?

Hi,

My friend bought some MCBs at a very low price. the problem is that they dont have stickers showing their ratings. i know it will work at 220V but what should i do to confirm its current rating? please suggest.

Thanks

Probably the easiest way would be to use a DC bench supply that has the ability to deliver an adjustable current. Set the voltage to some arbitrary level, say 5V, and adjust the current to the lowest setting. Then connect the circuit beaker directly across the voltage output of the bench supply. Then slowly raise the current until the circuit breaker "pops". Whatever the current level was when that happened is the current rating of the breaker.

Check the specs on the Bench Supply to see if there is an optimal voltage level for this experiment [i.e. if there is a voltage level that will insure the highest current range]. The voltage across the breaker, before it pops, will be around zero, but, just in case, check for an optimal voltage 'setting' that will produce the greatest current range.

http://www.circuit-protection.co.uk/latest-news/138-megger-makes-primary-injection-portable

so basically i need to connect the breaker's contacts to a load which supplies current. after setting the appropriate voltage, i need to increase the current and see where it trips. the current where it trips will be its rated current. right?

the device for this is called Injection kit. I know the breaker will be 63amp max. So, 0-100amp injector would be enough for me. Can you please help me find the right one? or make my own?

Thanks!

II’ve just given you a link


I wouldn’t attempt to make these yourself because tier are Safety regulations which have to be approved and if you test a unit and it faults You will then be liable so its best to buy one if you plan to do this , that way if anything goes wrong only the company that made either the breaker of the injection testing unit can be held liable and not you

Do it yourself and you risk prosecution if it fails especially at 63 amps or 100 amps , definitely would go out and buy one unless you are degree qualified and know exactly what your doing testing this DC wise is a No

I wouldn’t take that advice about using a bench power supply to do this either

There are big differences btw DC breakers and AC breakers I hope you are aware of this

No offence by the way but I wouldn’t entertain that suggestion specially when it comes to 2 phase and 3 phase further if anyone does insist that you carry out test on Ac breakers like this Id polity tell them to shove the job where it fits best its not worth the risk

Go and Buy one !! That’s the safest answer for you and your clients and yourself

"so basically i need to connect the breaker’s contacts to a load..."

No, not a load. A _power supply_ [or more accurately, a _current supply_].

But, the jokes on me for _assuming_. It didn't occur to me that this might be a high current AC breaker. A "bench supply" is *not* the way to go, as Mark made clear. So, I've got nothing

I was swayed by the word "miniature" -- my bad.

okay i searched for the injection kits, specially megger's.

http://www.megger.com/us/products/ProductDetails.php?ID=1460&Description;=

i need to check single pole AC breakers upto 63Amps


i also saw this one:
http://www.trtest.com/page.php?cid=30

as i am new to all this, please advice which one will be better?

I wasn’t t being funny Steve just in case you think this its because I know what some people will do just to set you up

They enjoy doing this and making fools of people who probably do their jobs quite well under normal circumstances They do it for a living in other words where you and myself possibly work their idea of work is walking into companies asking them to do a job and then asking them to carry out tasks which they know full well are dangerous and misleading After which they actually set you up for money or get you closed down This becoming quite common practice in the Uk now They thrive on it , more often than not they think or seem to think they are something quite special looking for the slightest possible mistake that you might make so that they can report you to trading standards , quite common or they pass this info onto health and safety for real stupid idiotic things that again wouldn’t ordinarily bother most people

On the other hand We cant stand them!! You must have been lucky because Ive had this as to have other business in the uk quite few times They are a real menace to normal decent businesses hence we actually hate their guts and mean cannot stand some of them On the other hand the things they should worry about they dont which more often than not are highly dangerous

They known for doing this all the time some of them

Most of this is down the age old problem of jealousy or they just dont happen to like the fact that your in bussiness so they pull this age old dirty tricks policy this is fast becomming the norm in this country Dirt refernces , no references at all and try and set bussiness up and visa versa interbussines , client , consumer manager against manager directors you name it

Nothing you can tell me about some of this even to the point of involoving you in a violent dispute they will try this as well to get you set up with a possible criminal conviction at the end of it

Real bloody Filth some them will even go as far as using thier youngsters to do very much the same thing This is also not uncommon in the UK Iy gets to the satge where you walk into a job look at it and then what you need to do is think about every possible inconspicous fault or set of problems you might be facing in case the sone of bitch is trying to set you up This is how bad some of this gets Why I dont rush around for people anymore I take may time and its cash if they want anything done No cheques No accounts Cash In some case I know refuse to do any work for them at all They know why as well

That why im pointing this out now

So Im not pointing fingers at you directly please dont take it that way Im just sick to death of the real trouble makers plenty of them thier are too

okay i searched for the injection kits, specially megger’s.

http://www.megger.com/us/products/ProductDetails.php?ID=1460&Description;=

i need to check single pole AC breakers upto 63Amps

i also saw this one:
http://www.trtest.com/page.php?cid=30

The idea is simple. Just connect the breaker to the injection kit's output and start increasing the current and see where the breaker trips.

as i am new to all this, please correct me if I am wrong. Also, advice which one will be better?

Thanks!

Hi Mark,

re: "I wasn’t t being funny Steve just in case you think this its because I know what some people will do just to set you up"

Not sure what you're referring to. I've taken all of your comments, in this thread, seriously -- at least the bits that I read, I typically don't read all of what you write, 'cuz it's so long and often off topic.

Also, didn't know you were trying to protect me -- again, probably because I typically stop reading once you go off topic.

That’s nothing new Steve is it lets face it plain old normal Steve " doesn’t pay attention Steve " Incredible !! Finally Steve reads some of my comments God I must be blessed today " something g miraculous has happened Steve read my comments

I read that one, too, so don't piss yourself

Definatley improving then Steve

I connected two 1000 watt lamps in parallel and connected them to AC 230v through a 6 amp breaker (confirmed known rating)

since current adds up in parallel connection and 2000 watts require 8amps, the breaker tripped!

Then I removed the 6amp breaker and connected a 10amp instead. the lamps lit perfectly!

I wanted to ask will this method be useful if i keep adding lamps in parallel and check till 63amp?

I found this method the cheapest than buying an injector kit.

I went successful till 10amps. Please advice

The resistance of a filament lamp is not linear. It increases [dramatically] as the filament heats up. So, this is not a reliable way to build a test load.

Also, will your mains supply deliver 63 amps? I don't know how it is in Europe, but here, most of our outlets are protected by 15, or 20 Amp breakers (30 or 40 for higher load appliances). And the max current that the transformer that supplies your house/lab might not be that high. If you're doing this in an industrial area, then you might manage it, but it's kind of dangerous if you don't know what you're doing!

I will be checking till 32 amps. Sorry i typed 63. And yes i checked my mains supply, it is 63amps breaker.

Also, if it isn't the reliable way, then please suggest some other way to build the load.

Thanks

Well, actually, the light bulbs, in conjunction with a way to measure the instantaneous current, might just work -- even better if a data logger is involved.

It's a matter of knowing the current at the moment the circuit breaker breaks.

Here's a thought -- if you have access to a number of circuit breakers of known value, you can use them to bracket in the value of your unknown breaker.

It goes something like this:

Say you have a 30 Amp breaker, put it in series with your unknown breaker [DUT] and ramp the current up by adding 1000W bulbs. If the 30 Amp breaker trips before your DUT breaker, then the DUT breaker is greater than 30 amps.

Next try a 40 Amp breaker in series with your DUT...then a 50 Amp... keep doing this until the DUT trips. At that point you know the DUT breaker has a trip point between the value of the final breaker and that of the previous breaker.

But, that approach may only be practical if you don't need to know the precise trip point.

OR, you can use this technique to get into the ballpark and then use some other method to hone in on the precise value (the advantage being that your test setup doesn't have to be as variable).

Also, in rebuttal to my previous comment regarding the efficacy of using lamps as test loads, if the voltage across the lamps is the same in both cases (i.e. when tested alone and when used in parallel with other lamps as a load) then the load they provide is predictable. But, at such high currents, more than likely, the voltage will decrease as lamps are added in parallel, in which case, not so predictable.

One way around that would be to use a variac to adjust the voltage across a single lamp down to the same voltage that is present across numerous lamps and then measure the current through that single lamp. Also, it would be wise to measure the current through each lamp, to make sure they're consistent.

Example: With three lamps in parallel, measure the voltage across the lamps. Then, connect a single lamp to a variac and adjust the variac voltage to the same voltage as was across the three lamp parallel combination, and then measure the current through that one lamp. This current, can then be multiplied by three to determine the three-lamp load current (assuming that all three lamps draw the same current).

Also, because line voltage can vary, make sure to monitor the voltage across the lamps at all times, and make adjustments (i.e. re-calibrate) as needed.

And, hopefully the labor involved in determining the trip point of these unknown breakers is worth the cost savings