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Parallel Earth Paths In Steel Re-Inforced Concrete
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<blockquote data-quote="binky" data-source="post: 343384" data-attributes="member: 490"><p>we have just converted a carpark to LED lighting which involved removing all the old metal light fittings and installing plastic IP units. We tested circuits before commencing work, and found afew small issues. Today we retested circuits and found R1 + R2 values have increased. Double checked lots of our connections but can't find anything wrong with those. We haven't changed the actual circuits or cable runs which are run in steel conduit and steel trunking with some form of shared earthing system - there's about 6 actual earth cables for 16 circuits, and large parts of the car-park are conduit earthed. Car park is 1970s build and on original wiring. After a good days head scratching and re-testing we are at a loss to explain increase in R1 + R2 values, though live testing for Zs seems to give significantly better results. So we suspect that metal fittings screwed to concrete via large metal screws has possibly been giving parallel earth paths via the steel beams and re-inforcing steel works. Question 1/ has anyone else ever encountered such a thing before, or am I barking up wrong tree?</p><p></p><p>Question2/ would parallel earths via structural steel be considered acceptable if delivering acceptable Zs values?</p><p></p><p>my opinion to Q2 is 'not really' even if the steel isn't going anywhere soon!</p></blockquote><p></p>
[QUOTE="binky, post: 343384, member: 490"] we have just converted a carpark to LED lighting which involved removing all the old metal light fittings and installing plastic IP units. We tested circuits before commencing work, and found afew small issues. Today we retested circuits and found R1 + R2 values have increased. Double checked lots of our connections but can't find anything wrong with those. We haven't changed the actual circuits or cable runs which are run in steel conduit and steel trunking with some form of shared earthing system - there's about 6 actual earth cables for 16 circuits, and large parts of the car-park are conduit earthed. Car park is 1970s build and on original wiring. After a good days head scratching and re-testing we are at a loss to explain increase in R1 + R2 values, though live testing for Zs seems to give significantly better results. So we suspect that metal fittings screwed to concrete via large metal screws has possibly been giving parallel earth paths via the steel beams and re-inforcing steel works. Question 1/ has anyone else ever encountered such a thing before, or am I barking up wrong tree? Question2/ would parallel earths via structural steel be considered acceptable if delivering acceptable Zs values? my opinion to Q2 is 'not really' even if the steel isn't going anywhere soon! [/QUOTE]
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