Critical power for hospitals: what HTM 06-01 asks of your standby generators
7 Nov 2026
A hospital cannot lose power. Theatres, intensive care, imaging, pathology, medical gas plant, lifts, IT and the telephone system all depend on it. In the UK the standard that sets out how hospital electrical supplies should be designed and maintained is HTM 06-01, Electrical services supply and distribution. It is a long document. This article covers the parts that matter for your standby generators, in plain terms, and the places where sites usually fall short.
PCAS has worked on hospital standby schemes across the North West and Yorkshire, including a 10MW multi mains, multi generator scheme at a hospital in Liverpool and generator and switchgear work at hospitals in Stockport, Chester, Preston, Manchester and Sheffield. This is the first in a weekly series on the HTM and what it means in practice.
HTM 06-01 grades every part of a hospital by clinical risk. The highest risk areas, such as theatres and intensive care, need a no break supply from a UPS, with the generators behind it to keep the UPS fed. For most clinical areas the standby generators are expected to restore the essential supplies within 15 seconds of the mains failing.
Fifteen seconds sounds generous. It has to cover mains failure detection, the engine starting, the alternator building up voltage and the breaker closing. Add a cold engine, tired batteries, a slow controller and a changeover panel that has not been exercised for months and it gets tight. On a multi set scheme the sets also have to synchronise with each other, which the controllers handle but which adds time if the settings are wrong. When we test a hospital set we test the whole sequence from mains fail to load on the bar, not just whether the engine starts.
The HTM expects the secondary power source to carry the full essential load with the largest generator out of service. That is N+1. If you have two sets, one must be able to do the job on its own. If you have three, two must.
It also asks you to look at everything between the generator and the socket. A single air circuit breaker, a single changeover panel or a single cable run is a single point of failure however many generators sit behind it. On the Liverpool scheme, multiple mains intakes, bus ties and generators mean any one item can be taken out for maintenance with the hospital still covered. On a smaller site the questions are simpler. Can you maintain the ACB without a shutdown? Is there a maintenance bypass on the changeover? Is there a connection point for a hire set?
The HTM asks for site fuel storage to cover 200 hours of full load running for each generator, with a local or day tank holding around 10 hours. Many older sites were built to smaller figures and have never been reviewed. Stored diesel also degrades, grows bacteria and picks up water, so the volume on paper is only useful if the fuel in the tank is clean. Fuel polishing and tank cleaning are part of a hospital service plan, not an optional extra.
The transfer system matters as much as the tanks. Pumps, level switches, alarms and the control panel that moves fuel from bulk storage to the day tanks need testing like everything else. We design and build fuel transfer control panels for multi tank hospital systems and they get the same maintenance as the generators.
The guidance is clear. Test each generator on load with the real building load every month for at least an hour, preferably two. Once a year run a full load test of three to four hours. The building load rarely reaches the full rating of the set, so the annual test normally needs a load bank. In between, carry out functional checks at least every three months: battery condition, coolant level, guards, alarms and the state of the plant room.
The annual test is the one that finds the real problems. Cooling systems that cannot hold temperature at full load, alternators with insulation breaking down, turbochargers and exhausts fouled with carbon from years of light running. A great many hospital sets only ever run off load. That is a test of the starter motor, not the generator.
Generator controllers and changeover panels age like everything else. A controller that is no longer manufactured, with no spares, is a risk in its own right. We upgrade older sets to ComAp InteliGen and InteliMains controllers, add remote monitoring so the estates team can see the state of every set from their desk, and test the full sequence including the return to mains and the retransfer delay. See our ComAp specialist and complex power control schemes pages.
Next in the series: load acceptance, step loading and sizing for N+1.
Call 0114 317 7939 or email support@pcasltd.com to talk about your hospital standby power.
Have a question about this article? Email support@pcasltd.com or call 0114 317 7939.
