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Terminal Blocks Minimum acceptable spacings for UL 1059

Application

Potential
involved in
volts

Minimum spacings in inches (mm) between uninsulated live parts of opposite polarity; and between an uninsulated live part and a grounded part including any mounting surface or exposed metal part

Through Air

Over Surface

Service – including dead-front switchboards, panelboards, service equipment, and the like

51 – 150

1/2(12.7)

3/4(19.1)

151 – 300

3/4(19.1)

1-1/4(31.8)

301 – 600

1(25.4)

2(50.8)

Commercial appliances, including business equipment, electronic data processing equipment, and the like

51 – 150

1/16^a(1.6)^a

151 – 300

3/32^a(2.4)^a

301 – 600

3/8(9.5)

1/2(12.7)

Industrial, general

51 – 150

1/8^a(3.2)^a

1/4(6.4)

151 – 300

1/4(6.4)

3/8(9.5)

301 – 600

3/8(9.5)

1/2(12.7)

Industrial, devices having limited ratings^b

51 – 300

1/16^a(1.6)^a

1/8^a(3.2)^a

301 – 600

3/16^a(4.8)^a

3/8(9.5)

Terminal blocks rated 601 – 1500 V^c

601 – 1000

0.55(14)

0.85(21.6)

1001 – 1500

0.70(17.8)

1.20(30.5)

Industrial, devices using the alternative approach to spacings^d

51 – 1500

As Determined By Evaluation^d

LED lighting equipment^b

51 – 300

1/16^a(1.6)^a

1/8^a(3.2)^a

301 – 600

1/16 – 3/16^a,e
(1.6 – 4.8)^a,e

1/8 – 3/8^a,e
(3.2 – 9.5)^a,e

NOTES –
1) A slot, groove, or similar spacing, 0.013 inch (0.33 mm) wide or less in the contour of insulating material is to be disregarded.
2) An air space of 0.013 inch (0.33 mm) or less between a live part and an insulating surface is to be disregarded for the purpose of measuring over surface spacings.

^aThe spacing between field wiring terminals of opposite polarity and the spacing between a field wiring terminal and a grounded dead metal part shall not be less than 1/4 inch (6.4 mm) if short-circuiting or grounding of such terminals may result from projecting strands of wire. Examples of means that prevent stray wire strand contact include rating the terminal block for solid wire only, and design features such as recessed terminal pockets.
^bThe spacings specified in items D and G are applicable to terminal blocks for use only inor with noted equipment types where the load on any single circuit of the terminal block does not exceed 15 amperes at 51 – 150 volts, 10 amperes at 151 – 300 volts, 5 amperes at 301 – 600 volts, or the maximum ampere rating, whichever is less.
^cThe minimum spacings on a terminal block rated 601 – 1500 volts shall not be less than the values, application E.
^d The spacing provisions in item F of Table 8.1 are applicable to a terminal block for use only in or with industrial control equipment where an alternative spacing evaluation is conducted in accordance with Section 39 of the Standard for Industrial Control Equipment, UL 508, andi the iStandard for Adjustable Speed Electrical Power Drive Systems – Part 5-1: Safety Requirements – Electrical, Thermal and Energy,UL 61800-5-1. Through-air and over-surface spacings are determined using the requirements in these Sections of UL 508 and iUL 61800-5-1, and are specified for each terminal block.

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Terminal Blocks Minimum acceptable spacings for UL 1059