New Viewpoint on A/C grounding

[chuck yahrling]

I came across this from a senior engineer at customer representing a major cruise line. Note the comment about A/C ground; I presume he is talking about conditons while underway.

'This particular ship we are talking about has six 4-Megawatt generators onboard which are "Grounded" to a 110,000 tons of steel. All 120V AC power is 3 wire single phase, and the outlet ground wire is attached to "Ship Ground", but obviously it's not a true "Earth Ground".

A simple meter to test AC outlets on land (showing Polarity, Opens, Reversal,etc) will show that there is an Open Ground condition on any shipboard AC outlet no matter how you wire it.
>
Technically the "Ship Ground" is a "Floating Ground" in relation to the hot/neutral sides of an AC outlet. In most cases this is sufficient for equipment to operate, however, it's not much better than not having a ground at all.'



cyahrlin@cisco.com

[Larry DeMers]

The situation on a steel ship of this size is totally different than any on a ship of our size. It is hard to understand any parallelism between the second hand *opinioins* that you parphrased, and the ABYC and NWFP codes that boats are required to adhere to. Certainly nothing new in technique that is translatable to our boats.

Larry DeMers
s/v DeLaMer
Cape Dory 30

I came across this from a senior engineer at customer representing a major cruise line. Note the comment about A/C ground; I presume he is talking about conditons while underway.

'This particular ship we are talking about has six 4-Megawatt generators onboard which are "Grounded" to a 110,000 tons of steel. All 120V AC power is 3 wire single phase, and the outlet ground wire is attached to "Ship Ground", but obviously it's not a true "Earth Ground".

A simple meter to test AC outlets on land (showing Polarity, Opens, Reversal,etc) will show that there is an Open Ground condition on any shipboard AC outlet no matter how you wire it.
>
Technically the "Ship Ground" is a "Floating Ground" in relation to the hot/neutral sides of an AC outlet. In most cases this is sufficient for equipment to operate, however, it's not much better than not having a ground at all.'

demers@sgi.com