Doubling up on shore power cable?

[PJHoffnet]

OK, first off - I'm going to say that I think I SHOULDN'T do this ... but I wanted a second opinion to see if my reasonable concerns might be too cautious. Can I use two 50ft shore power cables - connected together - as one long cable? My concerns are on the added resistance the longer cable length would cause.

41ft Maxum, 120V/50Amp. Shore power connection stern, stbd side in a tub on the swim deck.

I've always backed into slips, wte of one time I was just doing a short stop and went bow in, and a couple of side tie ups. With a 50ft shore power cable, I've never had a problem reaching the power pedestal.

Thinking ahead to some future trips, I've often wondered what I'd do if I did go bow in (or the pedestal was not at the base of the slip) and my shore power cable wouldn't reach the pedestal. One thought that came to mind was to connect two 50ft cables together (I have an older - in good shape - spare I keep on board) to make a 100ft cable.

So, let's let smarter minds prevail - tell me: Am a showing good concern, or am I a chicken?

 

[oscar]

I run a 100' cord on my motor home all the time. (2x 120/50A)

However, your concern is valid. Do you have a volt/ammeter? If not they are easy to install and it will give you an idea of what's coming out your end of that long cord. As long as voltage holds up and you are conservative on the current side (40A ish) you should be fine.

That said, please use very HEALTHY (new) cords. Any kind of corrosion/wear on a cord/plugs creates potential issues. Double the plugs and length and you quadruple said potential.

 

[Comodave]

I have used 2 50’ 30 amp cords together to make it 100’. It worked ok. I just watched the load and didn’t go near 30 amps.

 

[DavidM]

50A/240/120V shore power AC has much more give than 30A does, mostly because it is usually not operated at the limit. As long as you keep the power down near 30 or even 40A you should be ok with two 50' cords. Feel the connection for excessive heat.

David

 

[psneeld]

50A/240/120V shore power AC has much more give than 30A does, mostly because it is usually not operated at the limit. As long as you keep the power down near 30 or even 40A you should be ok with two 50' cords. Feel the connection for excessive heat.

David

I agree with David.

As background....

I have a 125/250V 50A set up and have run my 50 cord coupled to a 30 cord to a 30A shore power with no issues as long as I managed to stay below the 30A shore breaker. I know not the same but think through what you are doing and stick to a safe plan.

I wouldn't hesitate to combine 2 like you want to do in a second. Just manage the loads. Some may over worry, just the way some are.

 

[backinblue]

Manage the loads and if your cords are in good condition you should be fine.

 

[oscar]

Wow.... we have consensus. The doomsday engineers must be on vacation.

 

[Bacchus]

I've hooked 2 cords together frequentlywhen cruising and trying to reach a distant pedestal. As others indicated just watch for overloading.
I added a 25 ft cord to my supplies and find most times I can reach with 75 ft (50 + 25) especially if I run the cord fwd along the less used side deck to the bow and then to shore from the anchor platform. The 25 fter comes in handy for when pedestal is right at the aft connection area.

 

[Comodave]

Wow.... we have consensus. The doomsday engineers must be on vacation.

Ok, just to make you feel good, it will never work and the boat will burst into flames before you actually get them connected...

 

[backinblue]

Ok, just to make you feel good, it will never work and the boat will burst into flames before you actually get them connected...

That is much more in line with what I would expect to hear on TF!

 

[Comodave]

That is much more in line with what I would expect to hear on TF!

I just try to satisfy everyone.

 

[koliver]

Some of the docks that I get to get crowded. That means sometimes running a longer cable to find an unused outlet on the dock. I carry a couple of spare 50' 30amp cables, so can reach 150' if needed. That works for me, as I don't have many loads and am never drawing a full 30 amps in the busy season.

 

[Jeff F]

I added a 25 ft cord to my supplies and find most times I can reach with 75 ft (50 + 25) especially if I run the cord fwd along the less used side deck to the bow and then to shore from the anchor platform. The 25 fter comes in handy for when pedestal is right at the aft connection area.

Good idea. Lot of people could use 25' in their home slips.

My old boat had shore power connections bow and stern, which was really useful.

 

[AlpinaRanger]

Measure the voltage at an outlet. If you are at 110V or higher, you are fine. 108-109 maybe. 107V or lower, no bueno unless you are using a super low amount of amperage. Take a 1500W appliance. At 120V, you will draw 12.5A current. At 110V, you will draw 15A. So there lower the voltage, the higher the amperage. Also, if you are running a device with continuous high load such as a heater, you will need to increase the effective amperage by dividing by 0.8. In the above example, 12.5A will require a 16A and 19A circuit respectively. You might be surprised that measuring the voltage at the pedestals might not be that high depending on the wiring at the marina.

 

[MacPhid]

When joining two cordsets together I try to use sealing couplers to ensure foot traffic doesn’t loosen the connection.
https://www.marinco.com/en/510r
James

 

[SteveK]

Ok, just to make you feel good, it will never work and the boat will burst into flames before you actually get them connected...

The problem here is the OP said he did not think it would work. So of course everyone was ready to say that it will work. Is that reverse phycology?

Dave, I partially agree with you. Instead of 'before' it is more like flames after (about 48 minutes) you get them connected...

 

[tiltrider1]

The issue with adding a second power cord is voltage drop. Some one mentioned earlier to measure the voltage at the boat and see if it is 110v or 108v. As mentioned if the voltage is still 110v then there is no issue. Somethings like lights are just dimmer with voltage drop. Other things like motors can receive extra wear and tear or even be damaged by voltage drop. As is so often said, “you can get away with a lot of things until you can’t “.

 

[Comodave]

I was just trying to exaggerate as much as possible so I decided to have the boat burst into flames just by getting the power cords close to each other...

 

[ksanders]

The actual voltage is 120 volts.

There is no such thing as 110 volts.

The standard for power companies is 5% or 114 volts.

My personal opinion would be to feel the connections. If any of them feel appreciably warm then that connection is at risk.

If you want to extend your cord, fine, just limit your current.

 

[SteveK]

I was just trying to exaggerate as much as possible so I decided to have the boat burst into flames just by getting the power cords close to each other...

I know. Having some fun.

Kevin, I have given up on voltage in North America. I know it as 120 but a quick google search 110 and 120 are given as examples. A while back somewhere 108 was normal.
would you agree 5% less than pedestal at 100 feet is acceptable? That should not be noticeable warm.

 

[ksanders]

I know. Having some fun.

Kevin, I have given up on voltage in North America. I know it as 120 but a quick google search 110 and 120 are given as examples. A while back somewhere 108 was normal.
would you agree 5% less than pedestal at 100 feet is acceptable? That should not be noticeable warm.

It's funny but a lot of folks misunderstand the 110 vs 120 volt thing.

Here is a great way to think about it...

Take 120 volts. Multiply that times the square root of three and you get 208 volts. Reducing the phasor algebra in a 120 degree separated system results in the square root of three as a constant (1.73)

Now...

120 volts is an exact 1:60 ratio of industry standard 7200 volt phase to neutral distribution lines which are fairly standard in the USA.

That makes 240 volts a 30:1 transformer. For residential service take a 30:1 transformer and hang it on a 7200 volt line and then center tap and ground the secondary. This gives you two 120 volt legs with 240 volts between them. This is why we call it single phase power... because we connect it to a single phase of the distribution line.

Now... Take three 60:1 transformers and on the secondary side connect one side of all of thgem together and ground that. You get 120/208 wye which is a standard three phase service.

Take three 30:1 transformers and connect them in series, then take one of the transformers center tap and ground it. Now we get 240 volts delta with two 120 volt to neutral legs and one "high leg". That's what we call 240 volt "high leg" service.

Now try the same calculations using 110 volts as a baseline. The math does not work out.

As far as the 5% drop across the cord I would be cautious. The warm test is better than the voltage test. If you take a loaded down 120 volt line at say 114 volts and subtract another 5% you are at 108 volts. You are at that point into the range of potential unreliability. We have the 114 volts standard to take into account line loading, distance from a substation, etc...

As a public utility we generally have our substations operate in the 123.5-124.5 volt range at the substation. That gives us enough room so that the end of the line voltage during peak hour on peak day to be more than the required 114 volts.

 

[PJHoffnet]

Thanks for all the input. I do have a volt meter right at the power panel that gives voltage for both legs of the AC system.

I'll give the 50ft x 2 set up a try next time I'm doing some dock side work. Biggest AC load in port is always the air conditioners. I'll put both of them on and also the water heater - nothing else really draws much more power. I'll check the temp of the cables and connectors every half and hour, or so and report back.

 

[Ric in Richmond]

These will safely join the two and keep them from moving around...
I did that for years..

https://www.amazon.com/gp/product/B07XV9KBF1/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

Get the threaded rings that go with it. They will slip over the ends of the cable.

 

[Circumnavigator]

Some loss numbers at 120VAC

#10 wire - 3% at 3,500 ampere-feet. Therefore, a 100 foot cable will lose 3% if carrying 18 amps (200 feet round trip). Therefore about a 6% loss at 30 amps.


#8 wire -- 3% loss at 5,600 ampere feet. Therefore, a 3% loss at 28 amps.


I'd worry more about the extra connectors. Unless they are perfectly clean, connectors typically get a little warm, which is both a power loss and a potential hazard. Keep them really clean.


I have a spread sheet that does this kind of math for any wire size (0000 to #24) at 12, 24, 120, and 240 volts. Also for bolts and bus bars. Drop me a private message and I'll send it to you.


Jim



Jim

 

[MYTraveler]

I have been at plenty of (mostly foreign to USA) docks at which it was necessary to use a 75' + a 50' for my 50A/240/120V service. My biggest concern was the connection getting kicked into the water so I tied it down to the dock at the joint. Neither the connectors nor the cord ever felt particularly warm to the touch.

 

[L Erie Tugger]

The bottom line is that the 30 amp rating is the ampacity of the cable. That means that it will carry 30 amps without overheating. The connections are another question and must be in good condition on any cable length. The real question is voltage drop and the only way to check is a voltmeter. More common than a problem with your longer cable is voltage drop in the marina system. We sometimes see voltages in the high 90 volt range even with 25' cables. Be sure to turn off all motor-driven appliances (read AC's) when you see voltages much below 105.

 

[rolomart3]

According to calculations and my recollection a 50-foot number 8 wire while carrying 50 amps will drop about 1.5 volts dissipating 1.5 watts per foot (about the heat of a typical flash light bulb).
Since there are two wires everything doubles. So:
Doubling to 100 means a total drop of 6 volts and no change in the heat dissipation per foot ( twice the dissipation in twice the length) .
6 volts in a 240 volt circuit is below the 3% percent maximum recommended drop in boating (5% in residential).

A much more important concern than the wire length is the connectors. Make sure that the plug and receptacle blades are metal shinny and properly insulated with silicon paste.