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EarthNuts -- Speed up SWA armoured gland installation and EMI / RFI screening

Earthing Nuts F.A.Q.

1. Q. Are Earthing Nuts Patented?
A. Yes. Earthing Nuts are protected in the UK and Internationally by Patent application, No PCT/GB2005/003246.
2. Q. Should Earthing Nuts be supplied with brass screws instead of plated steel?
A. Earthing Nuts are supplied with steel screws for a variety of reasons, the main being mechanical strength especially with the smaller sizes using 4mm screws. There is little benefit in using brass screws except perhaps the resistance to corrosion. Contact your distributor for any special requirements.
3. Q. What size earth cables can be connected to Earthing Nuts?
A. Standard Earthing Nuts are made to accommodate many manufacturers’ crimp terminals for earth cables to table 54G of BS7671. For convenience earth cable and crimp lug sizes are shown in table 1.
4. Q. With what sizes of SWA cable can the armouring be used as earth?
A. PVC-SWA-PVC cable up to 4 X 400mm, 3 X 185mm and 2 X 95mm has armouring sufficient to comply with table 54G. XLPE-SWA-PVC cable has more sizes that need additional protective conductors. See Table 5 for clarification. Other cables may comply through closer calculation (BS7454, BS7671).
5. Q. I need to fit the gland to the cable before fitting it to the box, can I still do this?
A. Yes. Earthing Nuts are designed to be used either with the teeth or the smooth side facing the enclosure wall. The nut has a thicker section, as the gland size increases, enabling it to be tightened easier than the traditional lock nut. As the connection is effected by the grub screw there is no absolute necessity for the nut to be completely tight, although this is considered good practice.
6. Q. Can Earthing Nuts and associated glands be reused?
A. Yes. Once used the Earthing Nut can be reused, as it will not alter under normal conditions, although on metal enclosures the teeth will deform slightly, they will still retain adequate performance unless they are forcibly turned against an enclosure when tight. The nut should however be inspected for damage prior to re-use. As a bonus a well fitted and tightened Earthing Nut and gland will allow the gland nut to be undone to remove cable without turning in the hole. If the gland is not seriously distorted by an over-tightened grubscrew, it will re-thread on removal from the Earthing Nut and should therefore be able to be re fitted.
7. Q. What regulations apply to SWA and Earthing Nuts?
A. Chapter 54 of BS 7671 gives regulations on earthing and bonding. Reference can also be made to IEE Guidance notes 4 and 5 for clearer explanation in connection with fire and shock. Specifically regulations 413-02-06, 413-02-18, 471-08-08, 526-01-01, 543-02-02, 543-02-04 and 543-02-05 will be found to have relevance. Also BS 7454 (Short Circuit Calculation), BS 5467 & BS 6724 (Thermosetting Cables, XLPE) BS 6346 (Armoured PVC Cables). BS 951 shows where not to use earthing clamps (e.g. around armouring). The NICEIC publish a very useful guide entitled “Snags and Solutions Part One, Earthing and Bonding" which answers many questions.
8. Q. What if I want to connect a larger earth than normal?
A. For special applications where larger than normal earthing conductors may be employed, extra thick nuts are available by special order.
9. Q. Can Earthing Nuts be used with single cables?
A. Yes. Oversized Earthing Nuts are available by special order for use with single, armoured cables.
10. Q. Can more than one crimp lug be connected to each Earthing Nut?
A. Yes, ideally they should be fitted to the same securing screw, providing its length is sufficient. Larger Earthing Nuts (32mm and up) are supplied with a stud and nut enabling various thicknesses of lug to be accommodated, this also allows for easier assembly of multiple lugs to the nut, see photographs.
11. Q. Can the teeth alone be used for earth connection?
A. No. There must be a direct connection made to the nut itself. Although the teeth are designed to cut through paint on metal boxes, the thickness and composition of the paint can vary to such a degree that it is impossible to ensure a satisfactory contact every time.
12. Q. Can Earthing Nuts be used with other glands or conduit?
A. Yes, Earthing Nuts can be used with any metallic cable gland. When using the split type of SY armoured flex gland these can only be used with metal boxes as they employ a clamping action on the braid involving the enclosure wall. If using this type of gland tighten well and align the grub screw with the slot in the gland to ensure a tight fit. Top hat style SY glands such as those made by Wiska or Lapp, for example, are more suited to fitting with Earthing Nuts. For use with conduit, thread slightly longer and fit a lock ring instead of a coupler. Pass the threaded end of the conduit through the hole in the enclosure, fit the nut hand tight, then tighten the lock ring from outside.
13. Q. Can Earthing Nuts be used for EMI / RFI bonding to cable screens?
A. Yes, in combination with a suitable metal cable gland. The nuts are designed and type tested to give a secure, reliable, ultra low resistance connection between any metric BS conduit thread and any suitably sized cable and ring terminal. To ensure EMI / RFI screening to surrounding metal enclosures, the nut should be rotated at least 90o while in contact with the enclosure in order for the teeth to scrape off the paint entirely. This is easily achieved by partially tightening the nut just beyond hand tight and rotating with a spanner. With the paint removed at this point, the teeth will be in intimate contact with the surrounding metal and should be tightened up to achieve a satisfactory screening connection. Again a direct connection should be made from the earth terminal to the nut.
14. Q. What tests have Earthing Nuts undergone?
A. Earthing Nuts have been type tested to section 10.4.2 of BS EN 50262 and have passed to category B. This type test involves subjecting 300mm long cable and gland samples fitted with Earthing Nuts to short circuit currents for one second. The report states that the samples are likely to complete tests to category C should a higher capacity test plant be sourced in Europe and sufficiently strong cable samples be used for the test. The tests performed exceeded the ratings of category B and most approached those of category C before either failure of the test cable sample occurred or high current plant capacity was exceeded. 75mm Earthing Nuts had 38,000A passed without a hitch.
15. Q. Why are Earthing Nuts not ‘CE’ marked?
A. Earthing Nuts are considered to be passive and therefore do not fall within the scope of the Low Voltage Directive or other ‘CE’ directives.
16. Q. Can Earthing Nuts be used in hazardous areas?
A. Yes. As Earthing Nuts will only ever be used within an enclosure, in a hazardous area they are not within the hazardous environment and do not require ATEX approval. They offer significant advantages over conventional methods when used in these areas.

These FAQ’s and other information given on this subject are suggested as reference only and in no way seek to replace correct design expertise or installation skill. These guidelines are believed to be correct. No responsibility or liability is assumed for any loss or damage resulting directly or indirectly from any error or omission in the information given herein. We disclaim any such liability. Use of this information and any other given in connection with Earthing Nuts constitutes acceptance of this disclaimer.

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