A relatively large and dated commercial building has been sub-divided in to individual units. The original building had several DNO supplies some PME and some TT. It looks like the building may have originally been a cluster of separate buildings which are now all under the same roof. Each sub-divided unit has its own installation supplied from one of the original DNO sources. Whilst the wiring is separate they do share steel trunking and structural steel. One of the larger units which is TT is to be let to a company that will have a heavy IT dependence. Just thinking about the possibility of EMI due to the common connections. Any opinions?
The following spring to mind that may require further investigation regarding the basic arrangements:
Is there adequate separation of the TT "earthing zones" below ground from buried metalwork connected to other (in this case the PME) earthing systems? If not, it may well not be a "TT as assumed by BS 7671" - certainly, I'd be a little concerned regarding 442, and whether the power frequency stress voltages would actually be as stated for TT system in Table 44.1.
SPDs further to and related to issue to 1, but also does the larger structure have LPS - if so definitely required? Certainly with uncertainty over the situation regarding power frequency stress and 442, would be thinking SPDs are a no-brainer here with IT equipment.
Any issues with 542.1 - especially 542.1.3.3, not forgetting 411.3.1.1
BS EN 50310 would normally be used in buildings with extensive IT equipment installation. The optimum type of supply is a TN system, although TT is not precluded. Formation of a CBN and mesh bonding as per the standard probably highly advisable.
The following spring to mind that may require further investigation regarding the basic arrangements:
Is there adequate separation of the TT "earthing zones" below ground from buried metalwork connected to other (in this case the PME) earthing systems? If not, it may well not be a "TT as assumed by BS 7671" - certainly, I'd be a little concerned regarding 442, and whether the power frequency stress voltages would actually be as stated for TT system in Table 44.1.
SPDs further to and related to issue to 1, but also does the larger structure have LPS - if so definitely required? Certainly with uncertainty over the situation regarding power frequency stress and 442, would be thinking SPDs are a no-brainer here with IT equipment.
Any issues with 542.1 - especially 542.1.3.3, not forgetting 411.3.1.1
BS EN 50310 would normally be used in buildings with extensive IT equipment installation. The optimum type of supply is a TN system, although TT is not precluded. Formation of a CBN and mesh bonding as per the standard probably highly advisable.
