50'50 then split or split then 2 30's

[Doghouse]

Shore power question.

Ignore the cost of cords for a min, consider that I have both.
Here are the facts:

You have 2 30 amp circuits on your boat.
The pedistal has 1 50 Amp plug.

Which is better?
A. Running 1 50 Amp cord to a y splitter at the boat and feeding the 2 30 Amp circuits.

B. Splitting the 50 Amp to 2 30 Amp sockets and running 2 30 Amp lines?

Why?

 

[Paul]

Based upon pure conjecture

I have no imperical data to back this up - Regardless, here's my $0.02. Assuming the total load does not exceed 50A. The weak link in this equation will be the 50 splitter, adapter or power post.

I would use the spliter at the power post and run two 30A cords.
I beleive (don't flame me if this is wrong) that AC voltage drop is both a factor of the length of the run and the total surface area (e.g.number of strands) of the cable. a voltage drop over the length of a shore power cord will increase current draw

Two 30A shore power cords are presumably thicker then a single 50A and will presumably be better at mitigating voltage drop and handling higher current loads.

Regards,
Paul

 

[Dennis W.]

Separate circuits

Doghouse, Are you assuming that you have two isolated 30A circuits? Each power cord is designed and sized to deliver the proper voltage and amps at the end of the cord. The limiting factor will be the wiring on your vessel, not the supply to the vessel. Perhaps I don't understand what your real question is.

 

[tkanzler]

If your only consideration is voltage drop in the cord(s)

A 50A 125V (only) cord, which is 6 gauge copper (.5 ohms per 1000 ft), has less than half the DC resistance as a 30A 125V cord, which is 10 gauge copper (1.25 ohms per 1000 ft) of the same length. So for a 50 ft 6 gauge cord carrying 50A, voltage drop is about 2.5V (or just over 2% at 120V), while a pair of 30A cords, each carrying 25A, would drop about 3.1V (or 2.6%).

Since the number of connections remains the same, the impedance of those is independent of how long each cord is.

Higher voltage drop will only cause more current flow in induction motors operating under constant load, which could be a problem if you have large AC motors on board. I'd be more concerned with the voltage supplied (under load) by the marina - the ones I've tested seem to have pretty flabby voltage (voltage is all over the place as loads are switched in and out).

Oh, and 50A 120V only cords are a lot more money than a pair of 30A cords, but I'd personally rather deal with just one cord given my druthers.

 

[Doghouse]

Thanks for the info

Thanks that is the info I was looking for. I figured there would be a loss difference but did not know the calculation.

There is 1 extra conection in the 2 30A configuration as both ends of the 30A lines are connected 5 instead of 4 with the 50. Minor detail.

Thanks for proving that the difference is nominal resulting in only milliamps of loss. It would take years for the savings in electricity to exceeded the cost of the cord.