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300A fuse caught fire?

U

UGT

New Member
Joined
Jun 27, 2021
Messages
55
Location
Austin, Texas
My system has been up and running perfect for 2 months, no problems. This morning when throwing a switch on the transfer box that had my under the sink hot water heater in line the 300A slow acting fuse melted and caught the 2/0 wire insulation and the fuse holder on fire. I heard the inverter alarm and smelled smoke. Fortunately I was there to se a small flame coming from the fuse holder, turned off battery switch. If I hadn't been home and caught this could have been very bad. I thought the fuse was supposed to blow so the wire wouldn't melt or catch fire? Why didn't that happen? This wasn't the first time to use the hot water heater and previously there was no problem using it. Thanks for your help. George in Austinburnt fuse 1.jpgburnt fuse 2.jpg
 
Get rid of the Maxi style fuse and get a T fuse and holder.

Poor connection is the cause of your problem. All surfaces should be cleaned before assembly and you should source fuse holders with double terminals so terminals aren't stacked. One should also run at high amps at initial use, then re torque the connections.
 
UGT said:
My system has been up and running perfect for 2 months, no problems. This morning when throwing a switch on the transfer box that had my under the sink hot water heater in line the 300A slow acting fuse melted and caught the 2/0 wire insulation and the fuse holder on fire. I heard the inverter alarm and smelled smoke. Fortunately I was there to se a small flame coming from the fuse holder, turned off battery switch. If I hadn't been home and caught this could have been very bad. I thought the fuse was supposed to blow so the wire wouldn't melt or catch fire? Why didn't that happen? This wasn't the first time to use the hot water heater and previously there was no problem using it. Thanks for your help. George in AustinView attachment 150652View attachment 150653
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My guess is you had the 2/0 lugs on top of the stainless steel nut…
That turned the nut into a little heater element.

You want all connections to be directly connected together.
No washers, no nuts, nothing between the fuse and the lug.
Or, he fuse needs to be in contact with a bussbar that has provisions for the lugs to be connected.
 
When purchasing my T class, many people on here warned me about skimping on quality. I ignored them. The fuse holder I bought has the same issue yours has, clamping to plastic. I am glad you had this issue and that nothing went wrong. My purchase is going back to Amazon, proper fuses will be ordered.
 
Tulex said:
When purchasing my T class, many people on here warned me about skimping on quality. I ignored them. The fuse holder I bought has the same issue yours has, clamping to plastic. I am glad you had this issue and that nothing went wrong. My purchase is going back to Amazon, proper fuses will be ordered.
Click to expand...
Never noticed it doesn't have a metal base for the lug, good catch. Yes, that design is worthless, plastic will creep.
 
okay thanks. Will get the blue Sea T class fuse holder. Want to make sure I get the right T class fuse. What would be best slow blow or fast blow?
My system consists of (3) LiTime 24v 200ah batteries in parallel. 3000W 24v Giandel inverter. On the inverter it says 24V 150A input and 3000W output. Connecting wires are 2/0. Not sure of fuse size that I need especially after experiencing this failure. This fuse was 300A. Thanks again for help.
 
UGT said:
okay thanks. Will get the blue Sea T class fuse holder. Want to make sure I get the right T class fuse. What would be best slow blow or fast blow?
My system consists of (3) LiTime 24v 200ah batteries in parallel. 3000W 24v Giandel inverter. On the inverter it says 24V 150A input and 3000W output. Connecting wires are 2/0. Not sure of fuse size that I need especially after experiencing this failure. This fuse was 300A. Thanks again for help.
Click to expand...
2/0 with 90C insulation means a 200A fuse. You fuse for the wire, not the load.

Doesn't matter fast or slow.

Fuse size would have had no bearing on the failure you experienced as it was a failed connection.
 
Zwy said:
Never noticed it doesn't have a metal base for the lug, good catch. Yes, that design is worthless, plastic will creep.
Click to expand...
For the record, Blue Seas has a nearly identical ANL fuse holder that is also a lot of plastic. As others have said, I suspect the problem isn’t the fuse holder, but how the connections were made. If the lug was on top of a stainless steel nut, that was the failure point. Stainless steel is a horrible conductor and will heat up if you try to use it as one.
 
That’s scary,…..im not saying what you should do but I’m saying what I find prudent…. I have seen a few boats and RVs get toasted for the wrong fuses and/or wiring ….That is avoidable..but it’s not cheap.

Every fuse in my new system (8) is a blues seas class T.. 110A - 300A with correct fuse blocks…
# 5502 & # 5007……
some circuits have a Buss ( blue seas 187 series ) MRCB dc lever switch breaker next to the fuse for turn off ability for service and isolation …. Some use a large battery selector switch next to the fuse.
All do a Great job…

you got pretty lucky… that's great ?…good luck…
 
The Blue Sea Systems #5502 T class fuse holder is excellent. It holds torque/tightness better than most, but always check all electrical fasteners for tightness a few days later. South Bend Components makes very good reasonably priced T class fast blow fuses. I prefer “Littlefuse” brand but I’m not paying 3 times the price. There are truly opportunists out there. I snagged a few 300 amp fuses when I see them at a good price last year. Be sure and have a spare. I’m glad the magic smoke didn’t travel too far.
IMG_0704.jpeg
 
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Another Blue Sea, in a sea of blue cells, user here. You can tell they are a quality product as soon as you pick them up.

@UGT do you have any pictures of the wiring hooked up to your fuse? It may be helpful to show other what not to do.
I'm glad you caught it when you did.
 

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Zwy said:
Never noticed it doesn't have a metal base for the lug, good catch. Yes, that design is worthless, plastic will creep.
Click to expand...
That was the first thing I saw.

The nut goes on the bottom. A heavy washer next. Fuse on the washer, cables on the fuse, heavy washer, nut. Torque to spec. (You don’t tighten to the plastic- it’s only there to hold stuff still; you use a wrench and a socket and tighten the two nuts against each other.

My Class-T’s are on a copper bar from battery pos(+) and then a bolt through cable terminal and fuse. Not ideal but I only had to buy the fuses for each battery- everything else was on hand.
 
Skypower said:
The Blue Sea Systems #5502 T class fuse holder is excellent. It holds torque/tightness better than most, but always check all electrical fasteners for tightness a few days later. South Bend Components makes very good reasonably priced T class fast blow fuses. I prefer “Littlefuse” brand but I’m not paying 3 times the price. There are truly opportunists out there. I snagged a few 300 amp fuses when I see them at a good price last year. Be sure and have a spare. I’m glad the magic smoke didn’t travel too far.
View attachment 150728
Click to expand...
The 5502 are rock solid heavy beasts… have been using them for many years on boats… I even use them and the smaller # 5007 blocks for 160v terminal posts when it’s hard to find stuff rated over 48 volts as I need in my Anderson array disconnects… they have great customer service , product knowledge and actually call you back too.
 
To back up what everyone else has said, the biggest issue is stack up. With this style, you need the fuse in direct contact with the cable lug. Putting that nut between the fuse and cable lug was the source of your heat/fire/melty fuse holder.
 
UGT said:
My system has been up and running perfect for 2 months, no problems. This morning when throwing a switch on the transfer box that had my under the sink hot water heater in line the 300A slow acting fuse melted and caught the 2/0 wire insulation and the fuse holder on fire. I heard the inverter alarm and smelled smoke. Fortunately I was there to se a small flame coming from the fuse holder, turned off battery switch. If I hadn't been home and caught this could have been very bad. I thought the fuse was supposed to blow so the wire wouldn't melt or catch fire? Why didn't that happen? This wasn't the first time to use the hot water heater and previously there was no problem using it. Thanks for your help. George in Austin
Click to expand...
Fuses only blow when line amperage is exceeded. From your description of a rapid event of heat up and fire just after turning on (or off, not really clear based on your description) the switch leads me to suspect a seriously loose cable connection at the point of fire. DC voltages can create arcs that are able to weld steel. No type of fuse holder or fuse is immune from damage if it is not properly connected.

Your being home and throwing the switch is likely the precipitating factor rather than a long term heat up. Though that is something you should monitor on heavy load DC circuits.
 
Wasn't sure about the 300A fuse all along. I am now trying to decide on going with 175A or 200A. I am fortunate to have been able to shut down the system in time. From the posts above am convinced that the way I had the stack with the nut in between the two lugs was the problem. Shudda known better but now I do. My system is mostly used for backup in case the grid goes down here in Austin. With everything that is hooked up to my inhouse transfer switch I would pull abut 2800 watts and that is if everything runs at the same time. So thinking that the 175A would be enuff without experiencing blown fuses. I have a couple of 175A fuses that I had left over from my camper van solar system. Checked the fuse holder in the van I didn't make the same mistake with it. Thanks for the comments.
 
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