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-   -   100Amp fuse burnt again (http://www.diychatroom.com/f18/100amp-fuse-burnt-again-54506/)

hohadcr 10-05-2009 10:24 PM

100Amp fuse burnt again
 
this summer, when we just got the new place, we realized that left fuse out of the two fuses before the main breaker box was burnt. non of the breaker was tripped. We replaced the fuse, everything worked.

now it is cold again, and we started using some electrical heaters. Then, the same fuse (on the right hand side) out of the two before the main breaker box was burnt again! Some plastic around the fuse stand was burnt too. again, all the breakers in the breaker box was fine. We just replaced the fuse but we know that it is going to happen again.

What is going on with the electrical system, how should we start trouble shooting the problem?
Thanks a lot.

spark plug 10-05-2009 10:54 PM

Issue of burnt 100A. Main fuse. (1 out of 2)!
 
You most likely have an unbalanced load. That means, your loads in the house are not equally divided. That could be fixed fairly easily. First, visually. If after finding out which breaker goes to what appliance (or lighting circuit) you see that there are more appliances used on one side, just reposition the breakers. To get a more accurate idea, use an (inductive Ammeter) Over the main wires. Then reposition some breakers accordingly. (No matter what) :furious::no::drink:Don't Drink and Drive, Ever!!!

bobelectric 10-06-2009 05:49 AM

Burnt fuses usually indicate a loose fuse holder.

hohadcr 10-06-2009 07:57 AM

Thanks spark fuse, I will try to balance the breakers.

Thanks bobelectric, the holder is kinda loose, to change the fuse box, I am going to call the power supply company then.

AllanJ 10-06-2009 09:13 AM

Did you say burnt as well as blown?

You may need to carefully clean the fuse holder contacts and where they fit into the panel. You will need to achieve a good contact that is more than just a thin edge of one fin scraping the mating fin. Sometimes this is not successful and you would then need to replace the relevant components and possibly the entire panel.

Billy_Bob 10-06-2009 11:13 AM

There is how much electricity a specific breaker on one circuit uses. If too much on one circuit, the breaker will trip.

Then there is how much electricity all the breakers combined are using. If too much, then a main fuse will blow (breaker trip). And these are pretty much half on one main side and half on the other main side with the double breakers using both main sides.

I would suggest calling an electrician.

spark plug 10-06-2009 02:25 PM

Quote:

Originally Posted by AllanJ (Post 336965)
Did you say burnt as well as blown?

You may need to carefully clean the fuse holder contacts and where they fit into the panel. You will need to achieve a good contact that is more than just a thin edge of one fin scraping the mating fin. Sometimes this is not successful and you would then need to replace the relevant components and possibly the entire panel.

But let's take note that the OP said/wrote/ posted that the fuses were blown/burnt (in addition to being in such condition when he moved in) only when he started to run the heaters. (No matter what):furious::no::drink:Don't Drink and Drive, Ever!!!

Yoyizit 10-06-2009 05:04 PM

You can use your elec. meter as an ammeter.
http://en.wikipedia.org/wiki/Electricity_meter
Under
Reading electromechanical meters
if your wheel goes around in 1.08 second you are using 100A (at 240v) assuming you have the 7.2 factor as in the example.

If the fuses melt at nowhere near 100A then almost certainly it is a bad connection.

hohadcr 01-21-2010 11:52 AM

hey, everyone,

i did balance the circuit, but after a couple of month, it was burnt again.

this time, the fuse holder was really loose. I called in a master electrician, he said the problem was soly on the fuse holder in the fuse box....

he said that there was no such a thing as an unbalanced load, and everything run all into the two fuses.

So, is there not such a thing as an unbalanced load in the breaker box? :huh:confused.

Thurman 01-21-2010 12:10 PM

Technically, the Master Electrician may be correct in making this statement: "everything run all into the two fuses." The power coming into the two fuses will be a balanced load from your electrical supplier, or power company. BUT--after the electricity leaves the fuses and enters the bus bars feeding the breakers your power load does get distributed based on the total amount of amperage load on each bus bar. You could easily have six (6) 20 amp breakers on one side of your panel which would exceed your 100 amp fuse and cause the fuse to blow, theoretically. IMO--the "Master Electrician", while he was there and knew of the original problem should have ran a load test on your panel after the fuses, and before the breakers while the panel was under a full load. Thanks , David

Billy_Bob 01-21-2010 12:23 PM

It is pretty difficult to have a balanced load in a house!

That is because the homeowner turns on/off different things at different times.

In the evening you may be using electricity in the living room and bedroom and the load might be balanced.

Then on a Saturday you might be using the kitchen and washing machine and this might make it unbalanced.

If you have only one thing on, the load will not be balanced.

Now if you were a business and always had the same electrical things on during the day, you could equal out the load so it was balanced.

Say with a grocery store. They *always* have a lot of lights on. You could put one half of the lights on one circuit and the other half on the other circuit and balance it. (It is more complicated than that for a business, but that is the general idea.)

spark plug 01-21-2010 09:08 PM

Quote:

Originally Posted by Billy_Bob (Post 386658)
It is pretty difficult to have a balanced load in a house!

That is because the homeowner turns on/off different things at different times.

In the evening you may be using electricity in the living room and bedroom and the load might be balanced.

Then on a Saturday you might be using the kitchen and washing machine and this might make it unbalanced.

If you have only one thing on, the load will not be balanced.

Now if you were a business and always had the same electrical things on during the day, you could equal out the load so it was balanced.

Say with a grocery store. They *always* have a lot of lights on. You could put one half of the lights on one circuit and the other half on the other circuit and balance it. (It is more complicated than that for a business, but that is the general idea.)

Just to clarify my original statement to the OP. An unbalanced load does not mean that the Main Breaker or Fuse will trip. But when the load exceeds its capacity, which might be due to an imbalance, f.e.; 50/120, it might be a cause for blowing the fuse or tripping the breaker. But it's not the only one. As it turns out, that the Primary cause, in this case was a loose contact.:yes:!

AllanJ 01-22-2010 11:41 AM

If the contact is not that loose and you do not use that much current, then the contact is not going to get that hot.

But still get it fixed so you don't forget and turn on the heaters and have the panel damaged beyond repair.

An unbalanced load per se will not cause problems in a residential electrical system. What counts is no one fuse or breaker or other component being overloaded. In the case of the loose fuse contact, "overload" at that spot might be at 23 amps or maybe 7 amps even when the fuse is 100 amps.

tpolk 01-22-2010 12:04 PM

are we talking glass fuses and 2 fuses before the fuse box?


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