I recently had a power outage that blew one of our air conditioning fuses (which we were able to fix) and one of the fuses (out of two) in our spa equipment service control board. Next to both fuse slots it says 3 amps, but the fuse that blew had this written on it:

3·15A 125V
(it is about 19 or 20 mm long)

Does that mean its 3.15 amps, 3 amps, 15 amps? I thought it was supposed to be 3 amps since it clarifies that on the circuit board so I got a 3 amp 20 mm bussman fuse from Home Depot.

It came with two fuses and one blew like a firework so I don't want to put the other one in with the chance that there is a short circuit causing it. Any help would be appreciated.

Here are some pics Original fuse- https://i.sstatic.net/t5K8V.jpg Pics of the service panel circuit board--

Is there a short circuit or should I just try getting a 3.15 amp 125v fuse (instead of 3 amp 240 volt fuse)

  • 1
    Could you share a picture of the original fuse?
    – Camil Staps
    Commented Aug 27, 2014 at 18:37
  • Have you tried contacting the spa's manufacturer? I suspect you aren't the only person who's seen this symptom...
    – keshlam
    Commented Aug 28, 2014 at 1:12

2 Answers 2


3.15A is indeed an appropriate value for a BUSS GMA 5x20mm fuse.

Chances are something else is blown out. If you're not up to doing component level troubleshooting, probably a board will have to be replaced.

One part that frequently takes the brunt of power surges is MOV (varistor) devices, which look like big (often red or blue) ceramic disk capacitors.

enter image description here

It would be very close to the fuse, and, if there is a series fuse, will typically fail shorted so that when you replace the fuse it will blow again. The other possibility is that some kind of switching supply has failed shorted which would typically involve replacing semiconductors. Most service these days just involves tossing the module and replacing it, so you might want to check out the cost of a replacement board.

  • Hold do I check if it is blown (I have a multimeter) and if it is can't I just solder in a new one?
    – Jon Kimble
    Commented Aug 27, 2014 at 19:56
  • If it is blown it will be shorted (very low resistance) but you may have to remove it to test it properly. Yes a new one of similar type could just be soldered in. It should work without it, but it is not a good idea to leave it that way. Commented Aug 27, 2014 at 20:28
  • Ok I desoldered the varistor and replaced a 9 volt battery on the circuit board(i dont think it is related to this issue). I than put in my second fuse to test it and see if it was the varistor that was causing the blown fuses. After turning on power to the board, I again ended with the same blown fuse :(. any of you know what to do?
    – Jon Kimble
    Commented Aug 27, 2014 at 21:43

A quick google search lead me to this datasheet: http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/product-datasheets-a/Bus_Ele_DS_2017_GMA_GMA-V_Series.pdf

There is one part (GMA-3.15-R) that matches your description and the current rating is indeed 3.15A.

If you're wondering why the current rating is such a weird number, it's because it is a preferred number (Renard series):

R10: 1.00 1.25 1.60 2.00 2.50 3.15 4.00 5.00 6.30 8.00

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