Amperage reading....

[MikeP]

We've been having some trouble with shore power at our slip the past few days. The 240/50A service has been tripping the shore circuit breaker with the boat's ammeter showing 38-40A. When I talked to the marina office, the manager asked me if the boat's meter is reading Amps at 120 or 240VAC. I thought about that for a second or two and said, "I don't really know, I ASSUME it's reading amperage at 240 since that's what's coming into the boat but I don't know that for sure."

He suggested that maybe the ammeter is reading one side (120) of the two hots as opposed to the total current flow. I don't think that's likely at all since, if it was, that would mean the breaker is tripping at around 80A instead of 40A.

I shut off shore and turned on the genny with the same components operating. The Genny ammeter showed the same load for the same components as the shore power ammeter shows.

So...I BELIEVE that the problem is in the shore breaker. The shore breaker is not tripping at spikes, such as when the AC compressors cycle. It is tripping after a few minutes with loads beyond an indicated 38 or so Amps.

I suppose there could be a problem in my shore cable - excessive resistance for whatever reason. I guess I'll check that out.

Any thoughts re the issue or faults in my logic?

 

[Pascal]

First step is to feel for Heat around the breaker, plugs and the cord itself

Some cords are not tinned and will develop internal corrosion, getting warm under load

 

[MikeP]

I did that yesterday BUT it was cold/rainy so it's possible that any heat was dissipated by the "water cooling." I'm going to check out the cable/connections today. I'll also open up the cable itself and check the connections.

 

[doc g]

I just had shore power issues yesterday also....as far as your issue; resistance in the cord won't make your breaker trip at the dock. If you are tripping the breaker before whatever amperage it is rated at (50Amp I assume) it's the dock breaker. Yeah, the amp meters are 240V on the boat.....My issue was also dock related we went out and when we came back no juice in the boat with both 50 A cords plugged in. Checked at dock with meter 119 each leg , never checked across the two hots for 240. Chased that damn 119 all over the boat until I realized it stopped at the transformer. Evidently the X former does not know what to do with 120 volts . Plugged in at another source and all fine, not before wasting a few hours.......So what I had was two 119 volt legs coming in but not 220 which I need to run the boat........................Pat

 

[KPTIM]

Hi Mike,
I am sure your input power is arranged like my 1979 53MY. The on board amp meter reads the current on the 240 volt input side (in this case both lines L1 and L2 will read the same amperage as measured with a clamp-on style current meter). In this case the neutral wire (from the dock) is not connected on board. The grounding conductor (from the dock) is only connected as a shield to the ships transformer case. The boat power is supplied as 240 VAC not 240/120 VAC as in two separate lines (like are on some smaller boats that have two 30 amp services). Our boats have a transformer(s) that takes the 240 VAC in and makes it into 240/120 VAC to supply the ship's services some of the equipment 240 volt and some of the equipment 120 volt.

The only exception to this is if you have (like I do) the ability to plug into a single 125 VAC / 50 AMP dock power. In this case there is only one line voltage hot, the neutral is configured to the transformer and the grounding connector is used as the shield to the transformer case. In this configuration the transformer takes the incoming 125 VAC and generates 120/ 240 VAC.

When I was at your marina for a while I noticed others having problems like you are having. My bet (and from my experience) it is the main breaker in the panel that is failing. Most likely the contacts in the breaker are corroded or the trip/hold on spring is weak. In order to verify this they will need to bring in an electrician that has the capability of bringing in a load bank tester (or just change out the breaker). The other possible cause is your plug and or twist lock connectors are slightly corroded. Knowing the way you maintain your equipment probably not that.

Tim
KNOW PRESSURE

 

[saltshaker]

I just had shore power issues yesterday also....as far as your issue; resistance in the cord won't make your breaker trip at the dock. If you are tripping the breaker before whatever amperage it is rated at (50Amp I assume) it's the dock breaker. Yeah, the amp meters are 240V on the boat.....My issue was also dock related we went out and when we came back no juice in the boat with both 50 A cords plugged in. Checked at dock with meter 119 each leg , never checked across the two hots for 240. Chased that damn 119 all over the boat until I realized it stopped at the transformer. Evidently the X former does not know what to do with 120 volts . Plugged in at another source and all fine, not before wasting a few hours.......So what I had was two 119 volt legs coming in but not 220 which I need to run the boat........................Pat

Your transformer will give you 240V from the 120V source. Amperage will be half but the voltage will be there. You would need to connect to the 125V shore connection. Good to know for those rare instances when no 240V service is available. This is how I power my boat when on the hard and only a standard 15A Edison is available.

 

[doc g]

Mine would not . But I have a boost switch which I admittedly did not try . The way mine x former is wired it appears that it would only boost 208 . But as I said I did not try to boost the 120 to 240 ....Pat

 

[MikeP]

I tried a different 240/50A cable with the same results as far as the breaker tripping. The marina manager is going to have the 50A breaker changed.

 

[saltshaker]

Mine would not . But I have a boost switch which I admittedly did not try . The way mine x former is wired it appears that it would only boost 208 . But as I said I did not try to boost the 120 to 240 ....Pat

You should have a 50A 125V shorepower connection. You'd have to connect to that for it to work. You will not get 240V from the 250V shorepower connection when only 120V is available.

 

[KPTIM]

Hi Jack,
Sorry, On my 1979 53 MY I can connect to a single 125 VAC 50 amp outlet and have on board poere 240/120 VAC. On my power input station(s) on the boat I have three twist lock plugs two for 240 VAC 50 amp and one for 125 VAC 50 AMP. I know this because three weeks ago I was just at an older working marina waiting to go up on the lift and spent three days connected this way. Transformers can step up voltage as well as step it down. It is documented pretty well about this in my Hatteras literature and blueprints.

Tim

 

[saltshaker]

Hi Jack,
Sorry, On my 1979 53 MY I can connect to a single 125 VAC 50 amp outlet and have on board poere 240/120 VAC. On my power input station(s) on the boat I have three twist lock plugs two for 240 VAC 50 amp and one for 125 VAC 50 AMP. I know this because three weeks ago I was just at an older working marina waiting to go up on the lift and spent three days connected this way. Transformers can step up voltage as well as step it down. It is documented pretty well about this in my Hatteras literature and blueprints.

Tim

Yes that's exactly what I was saying.

 

[doc g]

I only have the two Glendenning Cablemaster 250v 50a inlets. I will have to re check my transformers and see if I can wire at least one of them with a switch to step up 125 to 250. Thx for the help....Pat

 

[rsmith]

The dock breaker is weak. Or it has aluminum wire as many do that's corroded

 

[oscarvan]

Can you reach another pedestal? Or move the boat to another location where you can plug in? Then see if you get the same result. My money is also on the breaker in the pedestal.

 

[MikeP]

Marina manager installed a new 50A breaker yesterday. I turned on sufficient elec to draw an indicated 48-50A on the boat's shore power ammeter and the new breaker did not trip. Clearly the problem with tripping at around 40A was a "tired" breaker.

 

[oscarvan]

Yeah!