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Discussion Starter · #1 ·
Someone had a problem in which their lights would dim when they would turn on a certain number of appliances. The apartment had 2 60A stick fuses. A friend of ours told us that when he tested each fuse, he got 110V. But when he tested the 2 fuses together, he got less than 220V. From this he figured that the fuses were going bad and when he replaced them the electricity no longer dimmed.

My question is -- why would the voltage go down for 220 if it didn't go down for 110 and what is happening with the resistance and amperage in the fuses that would cause that to happen?

Thanks.
 

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Fuses don't go bad. Most likely the issue was a poor connection on one of the fuses.
How much less than 220volts did he get. If the 110 volt reading were slightly inaccurate then I would consider 216 or 218 to be normal. Did he measure voltage to ground or to neutral. That could create some errors as well.
 

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JOATMON
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Your friend knows not what he is doing.

You basically have 240Vac service. Which means each leg is going to be around 110-120Vac. If he was not getting at least 115Vac, you 'might' have a line problem for the building where the voltage is a little low. Or, his meter may not be real accurate.

Considering he does not know what he is really doing tells me his equipment is suspect as well.

As to why it's working now? Either he tightened up a screw and didn't tell you or you still have a problem and you haven't seen it yet.
 

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Discussion Starter · #4 · (Edited)
He told us that when he measured the outgoing side of the 1st phase cartridge fuse to neutral, he got 120V. And the outgoing side of the second phase fuse to neutral, 120V. But when he measured from the outgoing side of 1 cartridge fuse to the outgoing side of the other cartridge fuse, he got around 6V. (If he measured from the incoming side of both fuses, he got 208V.)
 

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Sounds like this apartment building is supplied with 3-phase power, and each apartment gets a set of two of those three phases in different combinations, plus the neutral.
In this setup, 208, and not 240 volts hot-to-hot is normal.

The dimming of the lights most likely has to do with too many devices on the same circuit, undersized wire, or maybe a loose connection somewhere on the circuit, but it has nothing to do with those fuses.

The voltages and the fuses sound normal;

Please get a real electrician, have them inspect each circuit in the apt. and give you some recommendations.
 

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Mad Scientist
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Those voltage readings would sorta make sense if one of the fuses was blown, and the 120v measurement obtained from it was a backfeed from the other fuse via an electric stove, baseboard heater, or other 240v appliance.
 

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One of the fuses being blown would explain everything in this thread, and then it was replaced as described above and the problems went away as confirmed above.
 

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Fuses don't go bad.
Not so sure on that point !
Fuses that are run on close to there maximum for
extended periods do in fact deteriate !
I have had this problem before
usually if you replace both the fuse and holder
it's good again.
I would assume it is simply the resistance of the fuse element
and the fuse holder cotacts slowly increasing from the heat.
Fuses do tend to run a little warm.
 

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My question is -- why would the voltage go down for 220 if it didn't go down for 110

Thanks.
120V loads use the neutral 240v loads do not.
240v loads use two hots.

Also if your main supply is in fact 3 phase ? instead of split phase ?
then the phase angle between the two hot lines drops down to 120 degree's instead of the 180 degree's found on split systems.
This would account for the lower voltage.

Have you checked the voltage level at your main switch / isolator
before any switch gear.
This will tell you if the lower voltage is a poco issue
or an issue with your possibly over loaded system.
 

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A 6 volt reading is big difference from "he got less than 220V". That's basically zero volts.
The new voltage readings are definitely indicating a 3 phase 120/208 service and an open fuse.
 

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... Also if your main supply is in fact 3 phase instead of split phase ...
then the phase angle between the two hot lines drops down to 120 degrees (yielding 208 volts hot to hot) instead of the 180 degrees (240 volts hot to hot) found on split systems. This would account for the lower voltage.

Have you checked the voltage level at your main switch / isolator
before any switch gear.
This will tell you if the lower voltage is a poco issue
or an issue with your possibly over loaded system.
Nitpicking. The phase angle does not drop down depending on system load. For the 3 phase system the phase angle between the two hot lines is 120 degrees all the time.

Nitpicking. The full 208 volts hot to hot on a 120/208 volt 3 phase system is not a correctable* issue on the part of the power company.

* ... as in "needing to be fixed upon your demand", analogous to "plowable, needing to be plowed" or "payable, needing to be paid"
 

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Someone had a problem in which their lights would dim when they would turn on a certain number of appliances. The apartment had 2 60A stick fuses. A friend of ours told us that when he tested each fuse, he got 110V. But when he tested the 2 fuses together, he got less than 220V. From this he figured that the fuses were going bad and when he replaced them the electricity no longer dimmed.

My question is -- why would the voltage go down for 220 if it didn't go down for 110 and what is happening with the resistance and amperage in the fuses that would cause that to happen?

Thanks.
A few assumptions and this may have been covered above

Possibly since he is in an apartment the supply voltage to the building is 3 phase 208/120 and the supply to his unit would be single phase 208/120. So if he indeed had 110 VAC the Line to Line voltage would be 190 VAC.

Fuses do go bad the blow open, someone noted above fuse detrition and while this was a issue with older style fuses modern design from reputable fuse companies not avoid this issue. If you google Bussman Fuseology they state some where in their literature that their design avoids fuse fatigue, as it was often called.

The cause of the dimming was more than likely related to the fuse clips the tensioned clips that hold the fuse in place. There are simple way to test for loose fuse clips but as he has already replaced the fuses and the issue no longer exist testing is not feasible, though the issue will most likely return as weak fuse clips do not repair themselves magically.
 

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A few assumptions and this may have been covered above

Possibly since he is in an apartment the supply voltage to the building is 3 phase 208/120 and the supply to his unit would be single phase 208/120.
It would not be "single phase" if it is two legs of a three phase 208/120Y system, it would just be two phases of a three phase system.

Mark
 

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And it is called single phase 208 VAC
Two legs of a 120/208 volt 3 phase system used without the neutral would be 208 volts single phase. (Any two lines from an alternating current source would provide single phase power.)

But those two legs used together with the neutral should not be referred to as single phase. For brevity you could refer to this as part of a 3 phase system.
 

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Two legs of a 120/208 volt 3 phase system used without the neutral would be 208 volts single phase. (Any two lines from an alternating current source would provide single phase power.)

But those two legs used together with the neutral should not be referred to as single phase. For brevity you could refer to this as part of a 3 phase system.
Other than for a dryer or at the utility meter I can think of few cases where single phase 208 would have a neutral for the load.

But also remember in the trade many terms are used locally that have little or no meaning in other parts of the country. Though I believe in standardization of terminology as it does benefit us all.

But if you pull out your IEEE Dictionary of Standard terms it has 2 definitions under Single-Phase Circuit the first basically saying what you and I said.
 
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