OPTIMIZING 24 VDC POWER INSTALLATIONJerry Wick, Advanced Energy Industries, Inc.

Table of Contents

Questions and Answers 2

General Wiring Recommendations 2

Wire Gauge and Voltage Drop 3

Wire Gauge Recommendations 4

Stray Signals 5

System Troubleshooting 6

Environmental Conditions and Cooling 7

General System Recommendations 8

Recommended Four-Wire Gauge for Various Wire Length Runs 9

Recommended Two-Wire Gauge for Various Wire Length Runs 10

Proper wiring of AE products to the master 24 VDC

power supply can prevent a variety of problems. This

guide recommends specific wiring practices required

for consistent product performance. It assumes that the

relevant application has a main 24 VDC power supply

and the output voltage from this supply is distributed

to various devices located on or adjacent to the main

equipment. The tables on pages 9 and 10 provide

recommended wire gauge for various wire-length runs.

This is a guide to recommended practices. These

recommendations are not intended as mandates or

absolute requirements. Local and internal requirements

must take precedence as appropriate.

Products

• All AE power supplies

Applications

• Vacuum processing

Questions and Answers

The following section provides key questions and answers, assembled from numerous problem solving sessions and best-practice

recommendations.

Question

We use a common set of wires between the main power

supply and a distribution point. Individual wire sets then go to

each product. What wire gauges should we use?

2

Question

How can electrical power problems impact production?

Answer

Some negative effects include:

• No production (system or site down)

• Damaged output (product does not meet specification)

• Additional and unexpected maintenance costs

Question

Why should product/system wiring be designed

for performance?

Answer

Multiple power surveys indicate that approximately 80%

of all electrical problems originate within the facility. Only 20%

of electrical problems originate external to the facility.

General Wiring Recommendations

Question

What overall wiring method does AE recommend between

the main 24 VDC power supply and the AE product?

Answer

Each AE product should be individually connected to the

24 VDC power supply via dedicated wiring of appropriate

gauge. Wiring in a “daisy chain” pattern can cause issues with

equipment performance.

Question

Why does AE discourage the use of series-connected (daisy

chain) loads connected to the main power supply?

Answer

Series-connected equipment requires complex, detailed,

and careful load calculations. It would also require the use

of multiple wire gauges. For example, if the site requirement

were for eight 7 A loads, then:

a) The wiring between load one and load two is calculated for 7 A.

b) The wiring between load two and load three is calculated for 14 A.

c) The wiring between load three and load four is calculated for 21 A.

d) The wiring between load four and load five is calculated for 28 A.

e) The wiring between load five and load six is calculated for 35 A.

f) The wiring between load six and load seven is calculated for 42 A.

g) The wiring between load seven and load eight is calculated for 49 A.

h) The wiring between load eight and the power supply is calculated for 56 A.

Thus, the appropriate wire gauge grew from reasonable

to very large. Finding a series of power connectors that

can accommodate this range in wire gauge would be

extremely difficult.

Answer

Carefully sum the peak currents from each product. Use a

conservatively high current listing to determine an acceptable

wire gauge between the supply and the distribution point.

Use individual product peak currents to determine what wire

gauges should be used between the distribution point and

each specific load.

3

Wire Gauge and Voltage Drop

Question

Why is it important to use the recommended wire gauge?

Answer

Wiring without sufficient current-carrying capacity results in

excessive voltage drop. This reduced voltage, if even for a few

milliseconds, may cause the using device to report “low input

voltage” or not to operate as expected. Voltage drops can

cause anomalous product behavior.

Question

What is the significance of the voltage lost between the power

supply and the AE product?

Answer

Most AE products are designed to function with a nominal

24 VDC ±10% input voltage. If there is excessive voltage

drop in the wiring, the product has insufficient voltage to

correctly function. The lower voltage substantially decreases

the product’s ability to ride through any externally caused

24 VDC voltage reductions. Energy storage in a capacitor

is calculated as 0.5CV2. Thus, seemingly small changes in

voltage cause dramatic changes in total energy storage. The

product typically reports an input voltage failure and likely will

not operate as desired when the voltage does drop below the

allowable minimum.

Question

3% of 24 V is only 0.72 V. Why does such small voltage drop

matter?

Answer

A 3% drop is 30% of the total 10% allowable drop, a significant

reduction in operating margin.

Question

Can I gain any actual input voltage data from equipment that

is already on my site?

Answer

Possibly. Some AE products have an input voltage logging

function already in their software. Where available, this

monitor function can be accessed using AE Virtual Front Panel

(VFP) software.

Question

What maximum current is recommended for some common

wire gauges?

Answer

Please refer to the following table.

Table 1. Maximum current recommendations for common wire gauges [1].

Wire Gauge Max Recommended Current

24 6

22 8

20 10

Wire Gauge Recommendations

4

Question

What assumptions did AE make in providing the wire

gauge recommendation/run length distance tables

on pages 9 and 10?

Answer

This guide assumes that the main supply output voltage

is 24.000 VDC measured at the output terminals of the

supply. The recommended wire gauge tables are based on

an allowable 3% voltage drop. There are two sets of tables.

One set of tables is for cases in which there are two wires in

parallel for both the positive and negative conductors. The

other set of tables is for cases in which there is just a single

wire for each polarity (positive and negative). No remote

voltage sensing is assumed.

Question

Why do the wire gauge/run length distance tables, on pages

9 and 10, stop at approximately 30 m (100') length?

Answer

The 30 m distance accommodates the vast majority of actual

use at most installations.

Question

What product current (peak, instantaneous, nominal,

inrush, other) rating do I need to use with the tables

on pages 9 and 10?

Answer

Use the peak or maximum current rating. Do NOT use

nominal or steady state values. You do not have to use

maximum inrush current rating.

Question

My equipment voltage specification is 24 VDC ±5%. Can I use

the tables?

Answer

Yes. The tables are set up to provide a 3% voltage drop.

Question

How does the AWG wire gauge listed in the tables compare in area to either circular mills or millimeter squared dimensions?

Answer

The following information is identical to that in Table 8 in the NEC® Handbook.

Table 2. Wire size equivalents [2]

Size in AWG MM Squared Circular Mills

18 0.823 1620

16 1.31 2580

14 2.08 4110

12 3.31 6530

10 5.261 10,380

8 8.367 16,510

6 13.30 26,240

4 21.15 41,740

3 26.67 52,620

2 33.62 66,360

1 42.41 83,690

Stray Signals

5

Question

Does AE have any recommendations for situations in which

the 24 VDC wiring must pass near RF cables and products

(stray signal pickup defect)?

Answer

Small-amplitude RF can be eliminated or greatly reduced

through the use of ferrite beads or cores. The power wiring is

run through the center of the bead/clamp. Use steel conduit

to shield the power wiring if RF coupling to the 24 VDC wires

is an issue. Use of flexible conduit is not recommended as a

solution. Please note that a key assumption is that the power

and RF wiring is already separated from the 24 VDC wiring as

much as possible.

Question

How can I tell if the electrician installed the desired type

of steel conduit?

Answer

Test with a small magnet. A magnet sticks to steel.

Question

I observed excessive process-related signals on the 24 VDC

power wiring. What solution does AE recommend?

Answer

Do both pieces of equipment share either power or signal

wiring? If moving power or signal wiring causes the observed

signal to vary, the problem is caused by radiated emissions.

Physically separating the wires is a low-cost aid to reduce

the induced signal pickup. The following method to create

low-cost twisted-pair wire may help if the radiated noise has

a frequency of less than 500 kHz.

Twist the wire approximately four to six turns per foot to

create cables that can reduce stray AC or low-frequency

magnetic pickup. The wire twisting causes the noise to

become common mode. Common mode noise is reduced

at the downstream transformer.

Wire shielding or other EMI reduction techniques provide

solutions if the two items share common I/O or power.

Verify that you have correctly found the actual sources by

turning equipment off. You do not have the correct source

if the signal doesn't go away.Question

What distance between products do you recommend,

with RS-232 wiring?

Answer

The original RS-232 standard (1962) states a maximum

15.2 m (50') distance. Today, longer distances are often used,

with some data integrity issues. Low-capacitance wire and

wire shielding, as well as attention to wire routing, often

results in good performance. Very long runs may also use

electronic boosters to amplify the signal.

Question

I see stray RF or process signals when I monitor the RS-232

wiring. What solutions do you recommend?

Answer

If wire separation hasn't reduced the signal pickup sufficiently,

use RS-232 cable equipped with an outer shield to reduce any

stray signal pickup. Connect the cable shield to earth ground

at both ends if total cable is longer than 3 m (9.8').

Question

Does AE recommend any wiring separation distance between

wiring used for different functions?

Answer

A rule of thumb is that a separation of 2" (5.1 cm) or more

often substantially reduces any signal cross coupling. This

practice typically provides sufficient voltage reduction

for most AC and RF cables.

Question

How do I arrange two different types of wires that need

to cross?

Answer

All wiring that needs to cross should do so at a right angle.

This minimizes stray signal pickup. Always follow the

2" (5.1 cm) minimum separation rule.

6

System Troubleshooting

Question

The system worked acceptably for a reasonable period of time.

Suddenly, performance has been inconsistent. Any thoughts

or suggestions?

Answer

Something has probably changed. What events happened

at the date of the failure? A common problem is that an

inadvertent change caused the failure. Has anything on the

tool, cables, or other nearby equipment been moved or

added? Did the system start running a different recipe? Were

any product or system covers removed or not installed using

all hardware?

Use only known (measured) facts when troubleshooting. This

approach quickly leads to the true root cause. This structured

approach to problem solving may go by such names as

analytic trouble shooting or 8D, or another internal best-

practices term.

Question

We recently experienced inconsistent performance.

Any thoughts on possible causes?

Answer

Check to see if any periodic maintenance or cleanup was

scheduled. Verify that all switches are fully on/off in the

correct position and all cables are fastened. Keep a list of

settings or create physical marks to show the desired switch

positions. Always verify that all inner and outer covers are

installed using the proper number of screws.

Question

Several systems have what seem to be similar failures.

Any suggestions?

Answer

Is this a new failure mode? If the systems used to work

without defect, possibly some new or common factor is

causing problems. If different but identical systems have

near-simultaneous, identical issues, look for the common

factors. Verify both the AC and DC local power quality at a

point of concern. It's good practice to periodically measure

the delivered power quality at the point of use. If an anomaly

exists, it is important to know if this is a recent change or if

this parameter has always existed at this location.

Question

We routinely place any extra cord or cable lengths behind a product. Is this a problem?

Answer

The cords/cables can couple energy simply due to being in close proximity. We suggest that you separate the cords/cables to reduce the

coupling effect. Arranging the wire coils at right angles also reduces any signal coupling. The 2" (5.1 cm) separation recommendation

generally reduces the coupled signal amplitude to less than a critical value.

You can electrically reduce the wire/wire coupling by coiling the wire in a figure eight arrangement. This cord pattern is commonly used

in product conducted interference testing.

7

Question

We measured large swings in AC voltage at the point of use. Suggestion?

Answer

Determine if the same voltage swing is present at the power panel. If it is, it’s likely that the supplying transformer is undersized or has

excessive load. Check for both peak and RMS loads at the transformer output. Insufficient peak current capability typically manifests as

waveform “flat topping.” Also check for new or unknown additional loads connected to the power panel.

Question

We measured large swings in DC voltage at the point of use. Suggestion?

Answer

Determine if the same voltage swing is present at the tool power supply. If it is, the supply either is defective or has excessive load.

Check carefully for any short-term peak current load. Has any new or different equipment been added to the supply load? If the supply

performed acceptably in the past, then a very common problem is that the cooling fan may be defective or turning slowly. Another

common problem is a blocked air cooling path that causes the supply to overheat. If the tool power supply is connected to a “low” mains

voltage, check to see if the voltage select switch (if present) was inadvertently set to the high-voltage position. Finally, check the supply

electrolytic capacitors to see if they have an acceptable capacitance value, as they have a finite lifetime. Capacitors that are worn out

cause excessive ripple on the output voltage or large swings as the supply regulation circuit attempts to create and hold a constant output.

Environmental Conditions and Cooling

Question

The power supply will be located in a very warm environment.

The temperature might be close to the maximum ambient

product temperature rating. Do you have any suggestions?

Answer

Duct nearby cool air from an adjacent area to the air inlet

of the product. Use a fan to force air to the product if the

product does not have a fan. If a product fan is present, it can

pull the cool air via ducting.

Question

My company doesn't want to add any air ducting to our

equipment. The local area ambient temperature will be

approximately 55°C (131°F). What are some possible effects

from this planned usage?

Answer

We recommend operating AE products in accordance with

their ambient temperature rating.

Question

How much room do I need to allow for airflow at the fan

intake and exhaust?

Answer

The individual product manual should define the minimum

space required for airflow. A rule of thumb is that the gap for

both intake and exhaust airflow should be the same size as

the fan diameter, to avoid unnecessary restriction.

A necessary assumption is that the air intake has access to

cool air. It also should not be located near the hot exhaust of

another product. The hotter the air is, the shorter the product

lifetime is before failure or need for service.

8

Question

Does AE have any general recommendations for the 24 VDC

main power supply?

Answer

AE strongly recommends that any 24 VDC main power supply

be selected with “universal” auto-voltage VAC input capability

(85 to 264 VAC). Any power supply of this type should be

plugged into a 240 VAC nominal outlet when possible.

Question

Why should the main power supply be plugged into

a “higher” voltage?

Answer

The most common type of VAC power disturbance is a

temporary voltage reduction. This lowered voltage condition

remains for a fraction of a second. The auto-voltage select

power supply automatically switches to the “lower” voltage

range during this anomaly. The power supply automatically

switches back to the “upper” voltage condition once the

problem is not present. Result: The connected load(s) see

a constant steady state voltage and function without error

during the external power defect.

Question

Must I always consider using an uninterruptible power supply

(UPS) for powering either critical equipment and/or processes?

Answer

No. Most installations can mitigate the majority of expected

AC power problems with a properly sized line conditioner

or constant voltage transformer along with thoughtful

attention to on-site installation practices. A UPS should only

be considered where absolute power quality is mandatory

(for example, for a data center).

General System Recommendations

9

Recommended Four-Wire Gauge for Various Wire Length Runs

These tables assume two wires in parallel for both positive and negative polarity. Run length refers to the one-way distance between the tool

power supply terminals and the product use terminals along the path where the wires will be located (not line of sight). All wire lengths are

rounded to the nearest whole number.

1 A Load

Wire Gauge Wire Run Length

24 8 m (26')

22 13 m (43')

20 21 m (69')

18 33 m (109')

2 A Load

Wire Gauge Wire Run Length

24 4 m (13')

22 7 m (21')

20 10 m (34')

18 17 m (55')

16 26 m (86')

14 42 m (138')

3 A Load

Wire Gauge Wire Run Length

24 3 m (9')

22 4 m (14')

20 7 m (23')

18 11 m (36')

16 17 m (57')

14 28 m (92')

12 43 m (141')

4 A Load

Wire Gauge Wire Run Length

24 2 m (7')

22 3 m (11')

20 5 m (17')

18 8 m (27')

16 13 m (43')

14 21 m (69')

12 32 m (106')

5 A Load

Wire Gauge Wire Run Length

22 3 m (9')

20 4 m (14')

18 7 m (22')

16 10 m (34')

14 17 m (55')

12 26 m (85')

10 44 m (144')

6 A Load

Wire Gauge Wire Run Length

22 2 m (7')

20 3 m (11')

18 6 m (18')

16 9 m (29')

14 14 m (46')

12 22 m (71')

10 37 m (120')

7 A Load

Wire Gauge Wire Run Length

20 3 m (10')

18 5 m (16')

16 7 m (24')

14 12 m (40')

12 18 m (61')

10 31 m (103')

8 A Load

Wire Gauge Wire Run Length

20 3 m (9')

18 4 m (14')

16 7 m (21')

14 11 m (35')

12 16 m (53')

10 27 m (90')

8 41 m (134')

9 A Load

Wire Gauge Wire Run Length

18 4 m (12')

16 6 m (16')

14 9 m (31')

12 14 m (47')

10 24 m (80')

8 36 m (119')

10 A Load

Wire Gauge Wire Run Length

18 2 m (7')

16 5 m (17')

14 8 m (28')

12 13 m (42')

10 22 m (72')

8 33 m (107')

10

Recommended Two-Wire Gauge for Various Wire Length Runs

These tables assume a single wire for both positive and negative polarity. Run length refers to the one-way distance between the tool power

supply terminals and the product use terminals along the path where the wires will be located (not line of sight). All wire lengths are rounded

to the nearest whole number.

1 A Load

Wire Gauge Wire Run Length

24 4 m (13')

22 7 m (22')

20 11 m (35')

18 17 m (55')

2 A Load

Wire Gauge Wire Run Length

24 2 m (7')

22 4 m (11')

20 5 m (17’)

18 9 m (28')

16 13 m (43')

14 21 m (69')

3 A Load

Wire Gauge Wire Run Length

24 2 m (5')

22 2 m (7')

20 4 m (12')

18 6 m (18')

16 9 m (29')

14 14 m (46')

12 22 m (72')

4 A Load

Wire Gauge Wire Run Length

24 1 m (4')

22 2 m (6')

20 3 m (9')

18 4 m (14')

16 7 m (22')

14 14 m (35')

12 16 m (53')

5 A Load

Wire Gauge Wire Run Length

22 2 m (5')

20 3 m (7')

18 4 m (11')

16 5 m (17')

14 9 m (28')

12 13 m (43')

10 22 m (72')

6 A Load

Wire Gauge Wire Run Length

22 1 m (4')

20 2 m (6')

18 3 m (9')

16 5 m (15')

14 7 m (23')

12 11 m (36')

10 19 m (60')

7 A Load

Wire Gauge Wire Run Length

20 2 m (5')

18 3 m (8')

16 4 m (12')

14 6 m (20')

12 9 m (31')

10 16 m (52')

8 A Load

Wire Gauge Wire Run Length

20 2 m (5')

18 3 m (7')

16 4 m (11')

14 6 m (18')

12 8 m (27')

10 14 m (45')

8 21 m (67')

9 A Load

Wire Gauge Wire Run Length

18 2 m (6')

16 3 m (8')

14 5 m (16')

12 7 m (24')

10 12 m (40')

8 18 m (60')

10 A Load

Wire Gauge Wire Run Length

18 2 m (4')

16 3 m (9')

14 4 m (14')

12 7 m (21')

10 11 m (36')

8 17 m (54')

11

References

[1] Alpha Wire, Alpha Wire Catalog, Master Catalog Version 3A, Elizabeth, NJ: Alpha Wire Company, 1997.

[2] National Fire Protection Association, National Electrical Code® (NEC®) 2011 Handbook, Quincy, MA: NFPA, 2010.

©2013 Advanced Energy Industries, Inc. All rights reserved. Advanced Energy®, and A Powerful Advantage™ are U.S.

trademarks of Advanced Energy Industries, Inc. National Electrical Code® and NEC® are trademarks of National Fire

Protection Association {NFPA).

ENG-24VDCInstallation-260-01 0M 12.13

Advanced Energy Industries, Inc. 1625 Sharp Point Drive Fort Collins, Colorado 80525 U.S.A.

T: 800.446.9167F: +1.970.221.4670 www.advanced-energy.com

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Specifications are subject to change without notice.