This is made all the more complicated by the difference in terminology between AE and BE. In British English, we differentiate between 'earth' — literally connected to the Earth — and 'ground', which may be the local common reference point (also known as 'chassis', 'chassis ground', and 'frame') BUT may not necessarily be connected to literal earth!

So in your case, and if for a British readership, you could just say 'ground' — the consumer's 'ground' may be conencted to 'earth'. It gets a bit trickier in AE!

HOWEVER, that said, in more formal technical language, 'masse' is often used to refer to what in EN we call 'exposed conductive parts' (i.e. usually metal ones!) — in other words, all the metal bits of your device that ought to be connected to earth.

Now I don't believe your source text is using it that way, it sounds a much less formal sort of situation to me.

Do also be aware that in FR the terms are not always used with absolute precision: in the document I am currently working on, they are used at times interchangeably, which is an immense headache!

Also, please DO try and term search, as this must have come up several times before and you should have some very full answers already in the glossary.

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Note added at 2 heures (2016-02-05 21:35:57 GMT)
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BE: earth AE: ground

BE: ground AE: [chassis / frame / circuit ground]

BUT of course not all writers always use the terms accurately or worse still, consistently!

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Note added at 14 heures (2016-02-06 09:19:12 GMT)
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Possibly the most telling clue here is the fact that the s/t uses 'masses', while in certain usages it is non-countable.