Power Protection Products, Inc.

Grounding Loops

White Paper

by Dan Maxcy l 2013 Update

877-393-1223 I www.p3-inc.com

Grounding Loops

P3 is the industry’s trusted and respected critical power, cooling and energy solutions provider.

Quite often we here this term “Ground Loop” when searching for causes of equipment damage or

malfunction. Many equipment manufacturers and troubleshooters determine that ground loops are causing

their equipment to fail or not work properly. With this article we are going to explain exactly what a ground

loop is, how a ground loop can damage equipment and how to avoid ground loops.

A ground loop occurs in a power system when a path is provided for neutral current to flow into your

grounding system outside a proper neutral to ground connection. To illustrate this we will start with the

following power system diagram without a ground loop.

With Fig 1. diagram we can

see a transformer feeding a

Main Panel which also feeds a

sub panel and equipment.

The sub panel also feeds

equipment. At the output of the

transformer we have the

neutral to ground bond as

required by the National

Electrical Code and by IEEE

standards. This bond is very

important for both safety and

power quality purposes.

Under normal operation the

current flow in this system is

as follows. Current leaves the

transformer (Black arrow).

Flows through the Main Panel

and its circuit breakers (Black arrow). Through the sub panel into the equipment so that it may operate

(Black arrow). Neutral current then flows back from the equipment (White arrow). To the sub panel neutral

bar (White arrow). Back to the Main panel neutral bar (White arrow). And finally back to the transformer via

the neutral to ground bond. This is the proper way to design and build a power system.

The “ground loop” problem appears when multiple neutral to ground bonds are made. These other bonds

may be intentional or by accident. Let’s look at an example of a ground loop.

Notice on Fig 2. at the sub panel a neutral to ground bond. This is in addition to the neutral to ground bond

located at the transformer. This is not only a National Electrical Code violation but also a power quality

problem. By adding the multiple neutral to ground bond we alter the path for neutral current in the system.

Current now flows in the following manner.

Current leaves the transformer (Black arrow). Flows through the Main Panel and its circuit breakers (Black

arrow). Through the sub panel into the equipment so that it may operate (Black arrow). Neutral current

then flows back from the equipment (White arrow). To the sub panel neutral bar (White arrow). But now we

GROUND LOOPS By Dan Maxcy

2002 I� Revised 12/4/2013

Grounding Loops P3 Whitepaper

©2013 Power Protection Products, Inc. All rights reserved. No part of this publication may be used, photocopied, transmitted, or stored in any retrieval system of any nature, without the written permission of the copyright owner. www.p3-inc.com Rev 2013

1

Ground Loops Fig. 1

Quite often we here this term

“Ground Loop” when searching

for causes of equipment

damage or malfunction. Many

equipment manufacturers and

troubleshooters determine that

ground loops are causing their

equipment to fail or not work

properly. With this article we

are going to explain exactly

what a ground loop is, how a

ground loop can damage

equipment and how to avoid

ground loops.

A ground loop occurs in a

power system when a path is

provided for neutral current to

flow into your grounding system outside a proper neutral to ground connection. To illustrate this we will

start with the following power system diagram without a ground loop.

With Fig 1. diagram we can see a transformer feeding a Main Panel which also feeds a sub panel and

equipment. The sub panel also feeds equipment. At the output of the transformer we have the neutral to

ground bond as required by the National Electrical Code and by IEEE standards. This bond is very

important for both safety and power quality purposes.

Under normal operation the current flow in this system is as follows. Current leaves the transformer (Black

arrow). Flows through the Main Panel and its circuit breakers (Black arrow). Through the sub panel into the

equipment so that it may operate (Black arrow). Neutral current then flows back from the equipment (White

arrow). To the sub panel neutral bar (White arrow). Back to the Main panel neutral bar (White arrow). And

finally back to the transformer via the neutral to ground bond. This is the proper way to design and build a

power system.

The “ground loop” problem

appears when multiple neutral

to ground bonds are made.

These other bonds may be

intentional or by accident.

Let’s look at an example of a

ground loop.

Notice on Fig 2. at the sub

panel a neutral to ground

bond. This is in addition to the

neutral to ground bond located

at the transformer. This is not

only a National Electrical

Code violation but also a

power quality problem. By

adding the multiple neutral to

ground bond we alter the path for

Grounding Loops P3 Whitepaper

©2013 Power Protection Products, Inc. All rights reserved. No part of this publication may be used, photocopied, transmitted, or stored in any retrieval system of any nature, without the written permission of the copyright owner. www.p3-inc.com Rev 2013

2

Ground Loops Fig. 2

Ground Loops Fig. 3

P3 & PQU

www.p3-inc.com

For more information about our service plans and support services contact us at:

877-393-1223

1207 S. 75th Street, Omaha, NE 68124

Power Protection Products, Inc. (P3)

P3 specializes in representing only the best products and services that enhance power quality. By specializing the power quality, we can provide our customers with in-depth analysis, service and solutions that will meet the needs of our customers and end users. P3 works closely with your local market suppliers and vendors in order to provide you with convenient purchasing options, sales channels and follow-up service. We act as an extension of your current vendor base and work closely with your local market leaders in the power quality and electrical equipment area. In today's world of sensitive electronic equipment, power protection is no longer an option; it's a necessity.

Power Protection Products, Inc. provides the highest quality products and services available today that will protect and maintain your power supply as well as reduce your downtime, equipment failure and maintenance costs.

Learn more at PQU! www.powerqualityuniversity.com

Power Protection Products, Inc. is "showing you how" with Power Quality University

(PQU). Power Quality University brings real world electrical knowledge into the

classrooms. Students are taught the importance of power quality and the many factors which go into ensuring and providing good power quality. The instructors who teach at PQU are highly qualified professionals and are all experts in the field. Upon completion of a PQU program, students can obtain Continuing Education Credits (CEU's). PQU is just one more way that Power Protection Products, Inc. is affecting the electrical community in a positive way.