grounding needed?

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zyhml

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where 220/110(single phase, 220v with grounded neutral conductor) step down transformer feeds only one set control system in one rack including controller, meter and valves, would a grounding electrode connect to transform's enclosure or does a system bonding exist? As nec stated, step-down transformer seems not a separately derived system, so i can't find the applicable code for it. any reply is very appreciated.
 

don_resqcapt19

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Transformers, other than autotransformers, are separtely derived systems.
Don

edited to add left out word (are)
 
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zyhml

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but hand book stated An autotransformer or step-down transformer that is part of electrical equipment and that does not supply premises wiring is not the source of a separately derived system.
 

infinity

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Is this what you're looking for?

(3) Grounding Electrode Conductor, Single Separately Derived System. A grounding electrode conductor for a single separately derived system shall be sized in accordance with 250.66 for the derived phase conductors and shall be used to connect the grounded conductor of the derived system to the grounding electrode as specified in 250.30(A)(7). This connection shall be made at the same point on the separately derived system where the system bonding jumper is installed.
Exception No. 3: A grounding electrode conductor shall not be required for a system that supplies a Class 1, Class 2, or Class 3 circuit and is derived from a transformer rated not more than 1000 volt-amperes, provided the grounded conductor is bonded to the transformer frame or enclosure by a jumper sized in accordance with 250.30(A)(1), Exception No. 3, and the transformer frame or enclosure is grounded by one of the means specified in 250.134.
 

don_resqcapt19

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and that does not supply premises wiring
Almost everything that is not internal to equipment is premises wiring.
Premises Wiring (System). That interior and exterior wiring, including power, lighting, control, and signal circuit wiring together with all their associated hardware, fittings, and wiring devices, both permanently and temporarily installed, that extends from the service point or source of power, such as a battery, a solar photovoltaic system, or a generator, transformer, or converter windings, to the outlet(s). Such wiring does not include wiring internal to appliances, luminaires (fixtures), motors, controllers, motor control centers, and similar equipment.
Don
 

zyhml

Member
it seems the key issue is if a little system consisting of several valve and piping within very restrict area could be considered as a "equiment". if not, may i just use egc from supply side connecting step down transformer's enclosure and do nothing in transformer's sencondary side(110V)?
 

don_resqcapt19

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it seems the key issue is if a little system consisting of several valve and piping within very restrict area could be considered as a "equiment".
The wiring must be "internal" to the equipment to not be premises wiring.
if not, may i just use egc from supply side connecting step down transformer's enclosure and do nothing in transformer's sencondary side(110V)?
For the EGC to be of any value, there must be a connection to the secondary side of the transformer. If your installation does not meet the exception cited by Trevor, you need a grounding electrode, grounding electrode conductor and a system bonding jumper on the secondary side of the transformer.
Don
 
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