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Question DetailsAsked on 2/17/2014

how much does it cost to upgrade a 30 amp outlet on my boat slip to 50 amp outlet

I have a 30 amp outlet on my boat slip but I'd like to upgrade it to 50 amps. Would it be cheaper to just add a second 20 amp outlet?

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1 Answer


There are a few things to consider:

1) check your boat's system rating for maximum amperage - that may stop you right there, because adding one or more additional circuits and breakers in the boat so they don't show and meet marine standards is likely to be pricey.

2) if this is a marina type dock, check with management first - they likely limit each slip to a certain amperage outlet, and even if they allow upgrades likely require it be done by a specific contractor so they have confidence it is being done right.

3) check how the wiring is done - if there is a main trunk cable feeding a series of slip outlet breaker boxes, then to upgrade your capacity may require upgrading back to that trunk cable, or maybe only in the breaker box. In extreme case, the trunk cable itself might have to be upgraded if it is near capacity, which would be prohibitively expensive, but is likely the case if this is a marina where the electrical was installed along with the dock slips, where the cable would be rated based on the number of shore power connections installed at that time. If a private dock, same story- main feed cable to the dock was likely designed for 30A, not 50A - so would have to be replaced in entirety, or a whole new cable run to the dock for the added load.

4) Check local code - some codes limit a recreational boat to one shore power cable, others allow multiple. Generally only one feed allowed, plus most boats only have one shore power lead input point to receive the cable, and siamese cable connections, while available, are generally illegal for shore power.

5) Depending on the room available in the breaker box, may only require a new breaker and a new run to a second plug, if your current plug box is sized for multiple breakers. That would probably be cheapest in that case, as you are not changing anything of the existing system - just adding a second cable. However, if box has room for only one breaker and outlet, then upgrading that certainly is cheaper than putting in a larger or second box by itself. However, going to a 50A feed will mean upgrading the breaker, outlet, AND replacing your shore cable probably, or at least the connecting ends and the connection at the boat end if your cable is oversized, as each amperage rating has a different prong configuation. Therefore, total cost may well weigh in favor of a second feed cable rather than upsizing.

6) You will almost certainly need a Coast Guard inspection for any change to the boat or pier power - google this search phrase for referral to CFR sections and regulations regarding shore power - coast guard regulations on boat shore power cables

7) I have not done upgrades to shore power outlets, but I know from new construction projects that you are talking from 3-5 times the cost of equivalent house installation, because you are dealing with Coast Guard regs and inspections, plus dealing with NEMA Type 3, 3R, or 4/4X depending on specific design and local code requirements.

8) You knew what was coming next, I am surer - just too many variables, including type of existing power feed and connections and boxes, ength of trunk or feeder cable runs and cable sizing, etc - you need to talk to an electrician rated for marine work - and probably several for comparative bids, unless this is a marina that does its own wiring changes as almost all would. Don't forget you have to be looking at the entire picture from source into the boat, not just the shore power cable portion. My ballpark guess - several thousand $, PLUS any cost to upgrade the main feed cable if needed.

Answered 6 years ago by LCD

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