Preventative Maintenance

Planned Preventative Maintenance (PPM)

Has your LV Switchgear been installed and in use for some time? Have you considered Planned Preventative Maintenance? If you said “yes” to either, then please read the following documentation which has been compiled for your review. Please take the time to read this documentation and feel free to contact us if you required any additional information or further clarification, or direction.

Here at Underwoods we are also able to offer additional services to your LV infrastructure, so if you decide to delay your initial service you can still benefit from other aspects of our expertise, including spares, repairs, upgrades and New Switchgear.

Our maintenance works are offered on a single service basis, so you are not tied into any ongoing contract obligations. Each maintenance visit will be quoted on an individual basis, giving you the flexibility to plan your maintenance works to suit your sites requirements and budget.

Frequency of Maintenance

The frequency of your maintenance is crucial as the maintenance itself. We are continually asked how often we recommend that LV Switchgear should be maintained, with our customer hoping of a single sentence answer of “12months, or “as per manufacturers guide-lines”, but the truth is that the “frequency of your maintenance will be driven by the condition and type of equipment, our standard recommended maintenance on this equipment, and ultimately your Equipment Reliability Requirements (ERR).”

The ERR is spread over three levels for ranges of equipment.

•             High Reliability Required – i.e. Hospital Critical Life-Safety

•             Medium Reliability Required – i.e. General Power

•             Low Reliability Required – i.e. Non-Essential Services


Some of our customers, have products of a “high” reliability need, where devices supply power to say “a life-safety service”. A manufactures guideline would not take this into account and service would be carried out as per the guidelines, regardless of the condition of the device, or its reliability need. Standard maintenance could be every 2 years! However being “Life Critical” you may need it maintained and reviewed every few months.

At Underwoods, we understand that you live in a real working environment and that the condition of a device and your reliability requirements need to all be factored into a personalised bespoke maintenance package. A high reliability device, in poor condition may need to be maintained every month, where as a low reliability device in good condition, may in actual fact only need to be maintained every 4 years, not the standard 2 years.

During and after your initial service we will discuss what items within your LV Switchboard are to what ERR (Equipment Reliability Requirement) level, and from this we are able to tailor your maintenance to your individual needs, reducing costs and extending your LV equipment’s life span.

The following few pages, include tables, charts to further explain how we will interpret your information to build a personalised preventative planned maintenance program.

The Maintenance Frequency Matrix

The Maintenance Frequency Matrix (MFM) has been developed in parallel with the Frequency Of Maintenance Test (FMT), see table 2. Both of the tables have grown to encompass the Underwoods Engineered Products Ltd group of LV Switchgear products.

To utilise these tables effectively each item or item group in table 2, will have been allocated a Multiplier based upon the table 1 outcome of the item or items groups, its condition and ERR Level. This multiplier value is then used by both the Visual Inspection column & Visual / Mechanical & Electrical Comprehensive column, to give our recommended next visit.


Item 1, Range; Low Voltage Air Switch, feeding the LV Switchboard. 

Equipment Reliability Requirement (ERR) = (As indicated by you) 

After inspection by Site Service Engineer, Equipment Condition = Poor Multiplier value as shown in MFM = Medium x Poor = 0.5.   

FMT of a Low Voltage Air Switch = Ideal Visual = 2 (months).                                                                                                 

FMT of a Low Voltage Air Switch = Ideal (Full) = 12 (months). 


FMT of your Air Switch = Ideal Visual x Multiplier = 1 (months).                                                                            

FMT of your Air Switch = Ideal (Full) x Multiplier = 6 (months).


The above step-by-step guide would therefore indicate that this particular ACB would need to be visually checked every month, which could be carried out by a member of your staff, and should have a comprehensive PPM service every 6 months, carried out by a qualified member of Underwoods staff.

A personalised Recommended Frequency of Maintenance (RFM) is then produced and can be issued to yourselves for your LV Switchgear and from this you are to determine when to schedule the next maintenance and what specific items may require more attention than others.

On return visits to carry out the maintenance the same system is used and as your reliability needs change and the equipment improves from continuous maintenance, so does the frequency of the maintenance.

This culmination of historical testing and trending, will ultimately provide a quality Planned Preventative Maintenance for your LV Switchgear, and help prolong your LV Switchgears life expectancy.

What could happen without a PPM schedule;



















































Table 1

What could happen with a poorly organised PPM schedule;


(Frequency in Months)

 (Multiple These Values by the “Multiplier” in Maintenance Frequency Matrix (Table 1.)

Description (Range)


Visual & Mechanical & Electrical



Switchgear & Switchboard Assemblies




Low Voltage Cables




Low Voltage Air Switches




Low Voltage Moulded Case Circuit Breaker (Outgoing device)




Low Voltage Moulded Case Circuit Breaker (Incoming device)




Electromechanical & Solid State Protective Relays




Microprocessor based Protective Relays




Instrument Transformers




Metering devices




Earth-Fault Protection System




Low Voltage Motor Starters




Adjustable Speed Drive Systems








Battery Chargers




Low Voltage Surge Arresters








Capacitor Control Devices




Reactors, Dry-type




Engine Generator – Functional Test




Uninterruptible Power Systems – Functional Test




Automatic Transfer Switches – Functional Test



Table 2


What to expect from your PPM package;

The following pages will outline, by guiding you through which particular item of equipment can and could be serviced and to what level. We also outline how we will progress from our initial service to a full personalised Planned Preventative Maintenance Program.

As you are aware, your LV Switchgear is an important part of the daily running of the environment to which it serves. Unlike most maintained equipment, we cannot just switch the item off and begin work, so additional planning must be considered to allow minimal disruption. You should also be aware that any LV Switchgear should only be maintained by competent persons, as there is a risk of electric-shock and even loss of life and damage to equipment.

Our maintenance teams, have been trained to be aware of the dangers, however certain precaution and preliminary standards still need to be met. Please take the time to read the attached documents thoroughly and pay special attention to the “Notes & Exclusions” section.

The following few statements indicate what item ranges are associated with your LV Switchgear and to what type of service / maintenance we would be carrying out on them;

 Switchgear & Switchboard Assemblies;
• Paintwork degreased & cleaned.
• Vaccuum out.
• Interior Wipe Out.
• Busbar Transport Split Torque Test.
• Check Shrouding.
• Check Earth Bonding.
• Check Control Terminal Tightness (Pull Test).

  Air Circuit Breaker (ACB) – Withdrawable
• Exercise Breaker.
• Withdraw moving portion from Cassette, check operation of shutters, check operation of winding mechanism, wide out and re-grease as necessary.
• Check Auxillary Wiring.
• Check condition of clusters on rear of moving portion and re-grease as necessary.
• Check manual operation of moving portion.
• Clean mechanism and re-grease.
• Remove and Inspect condition of Arc Chutes.
• Inspect condition of Main Contacts, clean if necessary.
• Carryout Insulation Resistance Test.
• General wipe down and removal of foreign debris.
• Protection Module Trip Test

Air Circuit Breaker (ACB) – Fixed Pattern
• Exercise Breaker.
• Check Auxillary Wiring.
• Check manual operation of moving portion.
• Clean mechanism and re-grease.
• Remove and inspect condition of Arc Chutes.
• Inspect condition of Main Contacts, clean if necessary.
• Carryout Insulation Resistance Test.
• General wipe down and removal of foreign debris.
• Protection Module Trip Test.

Moulded Case Circuit Breaker (MCCB)
• Exercise Breaker
• Check Auxillary Wiring.
• Check Main Terminations (Torque Test).
• Check Shrouding.
• Check Interlocks.
• Trip Test Breaker.

Slimline Fuse Switch Disconnector
• Exercise Switch.
• Check Auxillary Wiring.
• Check Main Termination (Torque Test).
• Check Cable Protection Shroud.
• Check Interlocks.
• Check Fuse Terminations (Torque Test).

Combination Fuse Switch Disconnector
• Exercise Switch.
• Check Auxillary Wiring.
• Check Main Termination (Torque Test).
• Check Shrouding.
• Check Interlocks.
• Check Fuse Terminations (Torque Test).
Digital Meters & associated CTs
• Check Terminal Tightness (Pull Test).
• Check CT ratios are correct.
• Check CT Terminal Tightness.

Surge / Lightning Protection
• Check Status of Protection (i.e. LED or Flag status).
• Check Terminal Tightness.
• Check Protection Device.
Indication & Controls
• Check Terminal Tightness (Pull Test).
• Check Operation (where viable).

Power Factor Correction (PFC)
• Visual Check of Capacitors for failures.
• Check Terminal Tightness.
• Check Contactor & Step Fuses.
• Check PFC Controller Settings.
• Check Protective Device.
• Check Operation (where viable).

Change-over System (C/O)
• Carryout Test of Change-over system prior to PPM and after PPM.
• Check operation of Mechanical Interlocks (as necessary).


As a standard we offer three available time-slots for maintenance works to be carried out, these are designed to minimise disruption to your day-to-day running and to reduce expense. If however you require maintenance works to be carried out over multiple timed shut-downs, evenings, nights or bank-holidays, we are more than happy to price according to your needs.

PPM Visits;

Normal Working Hours, Mon-Fri 0800-1700hrs

Saturday Hours, Sat 0800-1700hrs

Sunday Hours, Sun 0800-1700hrs

Our offers, when quoted will include the maintenance works, based upon the previous details, tailored to your switchgear needs, including our traveling & mileage costs from our works. Please read the Notes & Exclusions section, for items that fall outside these costings.

Optional Extras

RFM (Recommended Frequency of Maintenance PPM Report

After carrying out our initial service, we will be able to recommend a time and cost for a return visit to carry on the next phase in your maintenance of your switchgear. How we allocate the frequency of your maintenance program is shown within the attached documents, if you would like a copy of our findings (RFM PPM Report) this can be offered as per below. This report can enable you to determine how often you wish us to carry out the maintenance works.

Record Drawing Revisions

After Carrying out our initial service, we will be able to determine how your switchboard is being used and what changes have occurred since dispatching the LV Switchgear from our works, or from a previous service. These changes may have been carried out by the electrical contractors, or changes in fuses and labeling by yourselves. Maintaining an up to date set of record drawings enables future works and upgrades to be carried out more efficiently and with less down-time and disruption.

Site Surveys For Future Works & Upgrades

We understand that the LV infrastructure of your premises is continuously evolving to meet new demands and ways of working. The Underwoods Group is able to offer a full range of services for future LV systems and equipment, from spare fuses & MCBs through to distribution & panel boards and on to LV switchboards, Control Panel, & Motor Control Centers. Please feel free to discuss your requirements.

Site Surveys For Maintenance Works On Third Party Equipment

During the life of your infrastructure of your premises it has continuously evolved to meet new demands and ways of working. Over time, various non-Underwoods equipment may have been purchased and installed, however these systems should also be maintained. As these items have not been produced by Underwoods, we would have to carry out a preliminary inspection and produce a report to assess its eligibility for maintenance, or replacement. Please feel free to discuss your requirements.


Recommend Spare List & Discounted Spares Rates

Certain elements of your LV Switchgear can be maintained by yourselves, if an outgoing fuse was to fail, then this item can be changed by a competent person, enabling your premises to maintain functional. We recommend that you keep a limited amount of spares on site, for just this type of incident. We are able to offer you a recommended spares list, priced below, which would offer your spares at a discounted rate.

On Site Training On Your LV Switchgear

LV Switchgear can be as simple as a fuse or could entail a complex Auto-Change-Over or Motor Driven Circuit, containing multiple parameters to set. When these parameters were set during of factory tests or on-site by the electrical contractors, they may have been set for an ideal environment. As your site has evolved so has the way certain aspects of your system should work, and we feel that you should have a greater overview and understanding of your LV Switchgear and what would happen in certain circumstances and how you can make the LV Switchgear work for you and your requirements.

Notes & Exclusions

  1. Underwoods Risk Assessments and Method Statements will be issued prior to attendance & must be approved before our attendance.
  2. Underwoods will not carry out isolation of LV/HV supplies, this must be carried out by others, at no costs to Underwoods. (If only local Isolation is possible, the level of PPM will be limited to suit).
  3. Underwoods will not remove any customer isolation i.e. padlocks, these must be removed by others, at no costs to Underwoods. (If padlocks removal is not possible, the level of PPM will be limited to suit).
  4. Permit to work will be issued prior to any works being carried out.
  5. Upon arrival at the location, we should have full and unobstructed access to the work area, where obstruction delay works, additional charges may apply at our current chargeable rates.
  6. When attending location, unexpected waiting time will be charged at the current flat hourly rate.
  7. The maintenance works does not include the repair of any damaged items, this would be assessed and a follow-up quotation issued.
  8. Minimum continuous work period charged is one full day (9 hours) including traveling.
  9. Cancellation of works should be made in good time prior to arranged date. Late cancellations will incur cancellation charges.
  10. When attending location, others will provide area lighting at no charge to Underwoods.
  11. When attending location, others will provide local power for hand tools 230/110V at no charge to Underwoods.
  12. Site inductions are limited to a maximum of 30 minutes and are chargeable thereafter at our current chargeable hourly rates.
  13. All facilities relating to Health & Safety at Work Act are to be provided by yourselves.
  14. Free of charge parking should be made available at location, alternatively parking will be charged at cost + 10% of the local parking rates at the time of the works being carried out.

Underwoods Engineered Products Ltd

PPM Servicing Team

Contact Us

Underwoods Engineered Products Limited

Unit 6, Brunswick Industrial Park,

Brunswick Park Road,

New Southgate,

N11 1JL

Phone: 020 8362 0226