Strange Electrical Fire

[knewell]

On Sunday, Steve and I were working hard to complete the Genset install on "Trim" which was focused on the Shore-Genset selector switch. The genset installed perfectly and we ran numerous sets of electrical appliances for many hours. We then completed the shore power wiring in which Steve copied the old 1979 color coding where black was gound!!!!!

Of course he didn''t let me know this and simply figured it was the correct method. Thus, when I plugged in the shore power, about 30 seconds later there was a large and loud explosion which blew our compass 2 feet of the binnacle and huge amounts of thick black smoke came from the helm area. Within 30 seconds, I had the shore power disconnected and Steve was spraying the fire extinguisher down into the pedestal where the compass came flying off as there was still a small fire burning inside the pedestal. After about 5-10 minutes we had the situation under control and a large group of people standing around trying to figure out what had happened and why the hell did there was an explosion in the pedestal.

After several hours of back tracking and finding that we (Steve) had sent 115Volts through our ground, we then knew the source of the problem. The thick black smoke came from our throttle and shifter cables due to the plastic coating burning off and producing all the black smoke. Strange enough, there was no other damage than the melted cables...no other wring was affected. About 5 hours later we had all of the system fixed and everything working properly, however we still couldn''t explain why the cables got hot and melted and why was there an explosion that sent the compass flying?!?!?

About 9pm last night while drinking heavily to recover from the excitement of the day, I realized that the throttle and shifter cable where the only paths to ground for the 115V AC via the rudder and steering cables. It seems that the 115V went through the engine and passed through the throttle and shifter cable, down the pedestal via the steering chain, into the steering quadrant to the rudder post!!!!!!!!!!!!!!!! The throttle and shifter cable simply heated-up under 30 amps in 30 seconds like a light bulb and melted the plastic off. The fumes from the plastic produced an explosive mixture with the air in the pedestal and combined with the hot cables, caused a small explosion which sent the compass flying like a small projectile!!!!!!

In the end, we only have about $100 worth of damage which is the cost of two new cables....which means we were really reallly really lucky with all considered.

Have you ever heard of such a thing happening?

[Silmaril]

Hmmmmm Black as GROUND???? Maybe NEUTRAL but NEVER ground!!!! Ground has always been green in AC systems.

And it also sounds like you do not have a main AC breaker, which is not a good idea. While you are at it, you should install a galvanic isolator, it will go a long way towards protecting your boat from stray currents. If you don''t have one, you will go through zinks at an alarming rate, like one a month, if you leave yourself "plugged-in". Not to mention the ghastly things that will happen to your underwater metals once the zincs have parted company.

It''s also a good idea to carry a small, plug-in AC circuit tester. That way you can check to make sure that wherever you plug in, some well meaning dock hand has not made the same "Black is ground" mistake that your friend did. They are cheap, like $15 and will give you peace of mind when you travel to other marinas.

[Silmaril]

OOOOOPPPPPSSSSS...White is NEUTRAL....geeze in the heat of the moment we all make mistakes sometimes!!!!

Sorry

[soapstone]

Sure, I''ve seen it in 3 phase systems. We once had an electrician get his color codes backwards. Was that way for years,,, until we connected two computers on opposite ends of the building with an older style of connection. There was 208 volts between the drains (signal grounds) It did similar.

I think this is why it''s such a good idea to either use an isolation transformer or to keep the grounds separate between AC and DC on mixed systems like a boat with AC.