12V Solar/Battery Q: Can I use glass fuse?

Thread Starter

foolios

Joined Feb 4, 2009
163
Nope, no luck. Okies, looks like takin' a trip back to the store. $19 was a sweet deal I thought. O well. Thanks for enlightening me on the importance of the difference between ac and dc fuses. I woulda never imagined you couldnt use a fuse for both applications.

Thanks again.
 

mcgyvr

Joined Oct 15, 2009
5,394
Nope, no luck. Okies, looks like takin' a trip back to the store. $19 was a sweet deal I thought. O well. Thanks for enlightening me on the importance of the difference between ac and dc fuses. I woulda never imagined you couldnt use a fuse for both applications.

Thanks again.
Not to mention the switch unit is probably AC rated only.. So you were SOL anyways.
Its the whole chain..weakest link thing.. It ALL must be rated for DC to be "proper"
 

Thread Starter

foolios

Joined Feb 4, 2009
163
Gotya, thanks.

Ok, just gonna use the sea switch that was recommended along with a fuse.

Thanks for your time, all.
 

alfacliff

Joined Dec 13, 2013
2,458
"who the hell are you"? I am an electronic technician with a lot of years experiance, and an ability to read the national electrical code. skin effect is interesting, but dosnt come into play till much higher than 60 hz. as far as zero crossing is concerned, that makes no difference. rms amps is the same as dc amps, or dont you read any of the books suguested for bsic eolectricity? if you have a heater element rated for 1000 watts, thats ac or dc.dosnst anyone know what rms means? the wire ratings mentioned are for voltage drops in dc systems. the voltage drop across a fuse is insignificant. a 2 amp fuse like an agc2 fuse is the same fuse whether used for dc or ac.
 

NorthGuy

Joined Jun 28, 2014
611
The difference between AC and DC is arcing. When you disconnect contacts, the arc forms in the air and it can sustain connectivity as you separate contacts, meanwhile producing lots of sparks and heat. It is not a big problem at 12V and 8A, but as you move to higher voltages and higher currents, this can easily destroy a switch which is rated for comparable AC voltages and currents, cause a fire or even kill a person operating the switch.

AC changes polarity 100 or 120 times a second, so the arc gets extinguishes at the next zero crossing. You barely can notice the arc when you disconnect the contacts and you don't even see it every time, only when you disconnect at the peak.
 

nsaspook

Joined Aug 27, 2009
13,087
DC rated fuses are tested for the ability to interrupt a sustained arc during a fault. The behavior is different in DC circuits even if the RMS current is the same.
https://www.youtube.com/watch?v=Zez2r1RPpWY
http://www.battcon.com/PapersFinal2003/UhlirPaperFINAL2003.pdf

If you're fusing even small RE batteries always use DC rated fuses/breakers and load disconnect switches. A 100Ah battery can easily have a 100A current during a short that will melt a non-rated fuse/fuse holder and wire to create a fire and arcing switches are just as dangerous.
https://www.youtube.com/watch?v=z0QhkuGClMw

http://www.cooperindustries.com/con...uct-datasheets/Bus_Elx_DS_2000_ABC_Series.pdf
 
Last edited:

alfacliff

Joined Dec 13, 2013
2,458
northguy, please do not sporead false information, ac does arc the time between cycles is not enough to extinguish the arc in a 50 or 60 hz system. an arc is a high temprature plasma effect, and there isnt tnough time to cool down enough to extinguish. ac switches relays breakers and such are all designed to either open fast enough or other means to extinguish arcs.just as high powered dc circuits are. check out "arc blast" on line for lots of pictures of what happens during ac arcs.
also, check out the fuse manufactrers websites, bussman and such for info on fuses, there are no dc and ac amp ratings for fuses only amps, except for ultimate ratings, which are affected by whether it is ac or dc volts, and some specialized fusesf for solar use on dc, which are not specified for ac use.
 

ErnieM

Joined Apr 24, 2011
8,377
The National Electrical Code is quite specific in calling for devices listed for the application they are used for.

Thus a device with only AC ratings may not be used for any DC circuit. Period.

Listed devices with a DC rating are available and those are the ones you should use, unless the work is not covered by code and losses are not covered by insurance. One such example is inside an RV vehicle.

You may be able to get away with schlock work using unlisted devices, but a few bucks under the table to the inspector may be necessary.
 

NorthGuy

Joined Jun 28, 2014
611
ac does arc the time between cycles is not enough to extinguish the arc in a 50 or 60 hz system. an arc is a high temprature plasma effect, and there isnt tnough time to cool down enough to extinguish.
My 50+ year experience in plugging and unplugging power cords tells me otherwise. Not once have I seen anything similar to the sparks you can get from 100V/10A DC. My guess is, you would have to go to 40-50A AC to get a similar effect.
 

k7elp60

Joined Nov 4, 2008
562
There has been a lot of discussion about fuses and circuit breakers. In my opinion the voltage rating on a fuse is important. I have a copy of the Littlefuse electronic designer's guide. I quote from the paragraph on INTERRUPTING RATING",Also known as the breaking capacity or short current rating, interrupting rating is the maximum approved current which the fuse can safely interrupt at the rated voltage." This tells me you do not want to use a 125V fuse on 12V, as it may not interrupt the circuit on an overload condition
Looking at the various characteristics of a 3AG fuse. The normal time for it to open on a over load is 4hrs for 110% of normal capacity. 5 seconds maximum for 200% overload of a fast blow, and 5 seconds minimum for a slow blow fuse.
The standard voltage ratings used by fuse manufactures for most small-dimension and midget fuses are 32,125,250, and 600.
I also have a copy of Siemens Technical Handbook that has characteristics of circuit thermal breakers. The maximum DC voltage rating for a typical breaker is 50VDC whereas the AC voltage is 250VAC.
I hope this reply gives some positive information to the readers.
 

Thread Starter

foolios

Joined Feb 4, 2009
163
I went to Home Depot looking for fuses, the guy in the electric department told me the fuse I bought for the switch is dual element, meaning rated for AC and DC.
Here is the item and it's description:
http://www.homedepot.com/p/Cooper-Bussmann-T-Series-30-Amp-Plug-Fuses-2-Pack-BP-T-30/100176555
In another description it states:
The UL-listed plug fuses have Edison bases and are rated for a maximum of 125 volts. Which could mean up to? But maybe includes 12v?
I am going to write to Bussmann and hope for a definitive answer. But then again it is probably a moot point if the PVNEC is saying absolutely no. I will look at that too.

Edit:
e-Mail sent. I'll post their reply when I get it.

Found this on the datasheet:
DUAL-ELEMENT, TIME-DELAY1 TO 30A125VAC OR LESS
http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/product-datasheets-a/Bus_Ele_DS_1034_T.pdf
This was listed under:
Fuses - Other Low Voltage
at:
http://www.cooperindustries.com/content/public/en/bussmann/electrical/products/supplemental.html
 
Last edited:

mcgyvr

Joined Oct 15, 2009
5,394
No the guy at the home depot doesn't know what he is talking about. Its NOT for DC use.

Dual element is simply dual elements that allow it to work better with short circuits as well as simple overcurrent situations.
 

alfacliff

Joined Dec 13, 2013
2,458
northguy, if your 50 years of experience has atught you that plugging and unplugging power cords makes bigger sparks on dc athan ac, you need a refresher on safety. plugging and unplugging live circuits is hazardous. and besides, if you are comparing ac power cords and battery dc plugs, batteries have a lot more current available than the normal ac power cord. not power, just current, due to the 120 ac receptical having a lot more resistance between the socket and current source.
 

Thread Starter

foolios

Joined Feb 4, 2009
163
The official response I got from whom may not be their technical expert, but here is the answer to the question I sent to Bussman(FUSETECH@eaton.com):

This fuse (T-30) is rated for 125Vac, not dc rated. So we may not be able to comment the fuse operation @12Vdc.
 

Thread Starter

foolios

Joined Feb 4, 2009
163
The official response I got from whom may not be their technical expert, but here is the answer to the question I sent to Bussman(FUSETECH@eaton.com):

This fuse (T-30) is rated for 125Vac, not dc rated. So we may not be able to comment the fuse operation @12Vdc.
Here's another little tidbit I stumbled upon over some time of keeping this in mind:
A Note on Voltage Rating

All fuses have a voltage rating. To maintain safety, this voltage rating should not be exceeded in application, although it is acceptable to use a higher rated fuse in a lower voltage application. For example: A fuse rated for 125 volts is appropriate in household (110V) or automotive (12V), while a fuse rated for 32 volts is appropriate for automotive (12V), but not for household (125V). Always replace a fuse with one of the same or higher voltage rating.

http://www.cooperindustries.com/con...oductsandaccessories/fuses/Glass_Ceramic.html
 
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