Conductors for Power

[Engineer22]

Given a three phase chiller, would it connect to a ground AND three conductors?

 

[GaryD]

Yes, I just verified on a one line diagram for a utility plant.  

 

[jakesaround]

The answer is maybe, yes, and no.

It really depends on the type of connection you have to the chiller, delta or wye.

If it is a standard 3 phase wye connection you would actually have 3 hot conductors 1 neutral and a separate ground connection.

If it were a typical delta connection you would just have 3 hot conductors and no neutral.

Typically the ground wire is not considered part of the supply wire bundle. It is a separate wire or just a connection point between the equipment and the system ground.

Hope this helps spark more thought into your question.

 

[Engineer22]

Responses very helpful- thank you Gary and Jake!

 

[jakesaround]

That drawing could indicate a 3 phase delta transformer with a center tap winding or it could be a diagram for a 3 phase motor.

Not all delta transformers are going to have the 4th wire "high-leg" which is the center tap ground/neutral conductor.

That is a variation that can be used when single phase loads need to be served from the same location.

See image below and I will include the link to the image as well for further reading.

https://ctlsys.com/support/four_wire_delta_circuits/

 

[Engineer22]

Thanks. So not all three phase services would have a ground? I assumed a chilller pulls alot of power, so it would be connected to 3 conductors + a ground.

 

[jakesaround]

Not all three phase services have a dedicated ground wire, that's correct.

Will a three phase chiller have a ground? Most likely it will always have a case ground and a four wire service with a neutral conductor.

Case ground protects the equipment and workers from damage and electrical shock hazards.

Whereas a neutral conductor is a return path for current imbalances, 3 phase systems, and is usually connected to the earth ground as well for general system/equipment protection.

Ground conductors and neutral conductors can be confusing because often times they are interconnected throughout the system but they actually serve different purposes.

Equipment like a chiller compressor or a motor is just another device that can connect to an electrical system in various ways depending on the design of the device itself.

The nameplate of the device should give details on the type of connection/service voltage it will accept.

Don't know if all this is helping or is just bringing up more questions but I hope it helps a little.

 

[Engineer22]

Hi Jake,

No, I appreciate all the info! I'm just looking for a general answer, nothing too specific. I assume for the most part it will have three wires and a ground, is that safe to say?

 

[jakesaround]

I would say in general it would be a 4 wire service with one wire being the neutral conductor and a separate case/equipment ground point.

 

[Engineer22]

I would say in general it would be a 4 wire service with one wire being the neutral conductor and a separate case/equipment ground point.

Thank you, Jake! Very helpful.

 

[BigWheel]

There are two types of grounds in an electrical system. You have the Equipment Grounding Conductor (EGC) and Grounding Electrode Conductor (GEC).

NEC Article 100 Definitions (Italicized text is my additional information):

Equipment Grounding Conductors (EGC) - The conductive path(s) that provides a ground-fault current path and connects normally non-current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both. This bonds the parts of the equipment that you do not expect to carry current under normal conditions (i.e., exposed metallic parts). This conductor is typically a bare copper conductor or has a green jacket or green jacket with a yellow stripe. This conductor is responsible for ensuring that all of the non-current-carrying parts of the equipment are of equal potential. This conductor does not carry current unless there is a fault condition. This is the "BONDING" conductor.

Grounding Electrode Conductor (GEC) - A conductor used to connect the system grounded conductor or the equipment to a grounding electrode or to a point on the grounding electrode system. This conductor is physically tied to earth (typically through a ground rod, but metallic plumbing direct buried in earth can be used, too). EGC are ultimately tied back to this point to provide a low-impedance path to ground in the event of a ground fault within the equipment. This is the "GROUNDING" conductor.

Three Phase Delta loads typically have only three phase conductors and a GEC that is somewhere near the three phase input terminal block. All EGCs within the equipment are tied back to this point as well.

Three Phase Wye loads typically have three phase conductors, one neutral, and one GEC. The Neutral is typically tied to the GEC and all EGCs are tied to this GEC. If a phase-to-phase fault occurs in the equipment, the neutral, which normally does not carry current under normal conditions, will suddenly carry current in the event of the fault; therefore, the Neutral is tied to the GEC and provides a path to ground that will not energize the exposed conductive surfaces of the equipment.

The picture you drew and provided above is called a "high leg delta" or "stinger." That type of connection is reserved for when you want to be able to tap a 240V single phase from a 480 three-phase service. Where I work, we do not permit high leg delta connections. On the rare installations where they exist, but have not been demolished yet, they are specially marked to alert the electricians of the potential danger.

I can't think of an installation where you would use a high leg delta on a purely three-phase load...in other words, I would not expect to see a three phase chiller pump connected to the source you drew above.

As a point of reference; some electrical systems have all six conductors! One example is a UPS-backed Power Distribution Unit, where the input feed from normal power would be a three phase wye source, complete with three Phase conductors, a Neutral conductor, a EGC conductor connecting the source panel and the UPS-backed PDU together, and a GEC tying the entire UPS-backed PDU and feeding panelboard to earth ground (Note that the panelboard is tied to earth through its own GEC as well). In effect, the source panel feeding the UPS-backed PDU and the UPS-backed PDU itself are both bonded together and solidly grounded.

All three phase systems will have a ground in one form or another (or both) - I think what you're asking is will all three phase systems have a grounded neutral. The answer is no. Purely three phase deltas do not have a grounded neutral, but high leg deltas and wye services do.