On 08/07/2017 02:02 PM, Carlos E. R. wrote:
I'm not familiar with the British electricity code. I guess it will be different!
Yes, start with that. (The not familiar part). There are a ton of differences in EU and North American power systems as far as physical structure. Its easy to be less familiar than you think you are. This stuff has become more than a little complex with the growth of grids. Neutral is tied to Ground almost everywhere in the US, if not on your house then on the next nearest pole or power pedestal. Ground rods are not universally used, because the rely on soil moisture content and can behave very inconsistently. During the dry season its common for some large networks to lose their ground because they relied too heavily on grounding rods which were no longer in good contact. Then there are differences between three wire systems (pos, neg, neut) and 4 wire systems (pos net neut ground) that occur in different parts of the world. Some parts of the US have individual houses all on one side (phase), and alternate every other house to the other leg to balance the phases. Then someone strings an extension cord. (Indications are that the US may slowly be moving toward a 4 wire infrastructure. https://en.wikipedia.org/wiki/Three-phase_electric_power But as far as These Tape Drives, this seems unlikely to be a ground issue unless some parts of the tape backup system are on the opposite leg. Electrical code frowns on this and wants all outlets in the same room to be on the same leg. There could also be large ground differences if some parts of the tape system are on a UPS and the other parts are Not, or are on a different UPS. A multi-meter can usually detect this situation for by checking for voltage between ground sockets between outlets. -- After all is said and done, more is said than done.