There have been many questions concerning time to bus, how that number is calculated, and what are some of the factors that can affect the value recorded. Below are some answers:

When does Blue Pillar record time to bus and how is that number calculated?

There are two different scenarios where Blue Pillar records a Time to Bus number. They are as follows:

1. During a load test event- A signal is sent to the ATS test circuitry through the Blue Pillar system. At the moment the signal reaches the ATS the time to bus counter starts. The timer continues to run until the ATS shows as connected to the emergency source.
2. During a power outage event- When the Blue Pillar normal power available relay drops out the time to bus counter starts. The timer continues to run until the ATS shows as connected to the emergency source.

It should be noted that all-time to bus readings are recorded locally at the piece of equipment and then reported up to the Blue Pillar server as a value. Recording values in this way eliminates any communication lag that may be present.

Factors Affecting Time to Bus Readings

When load testing there are many factors that can affect the time to bus number. It is important to remember that Blue Pillar is simply recording the time it takes from the time the test signal gets to the ATS or from the time the Blue Pillar normal power available relay drops out to the time the ATS shows connected to the emergency source. The Blue Pillar system is simply reporting that value and has no control over that process. Below are a couple of things to consider about time to bus:

1. How long does it take the engine to start and ramp-up to voltage?
   1. On a cold day, an engine that does not have an operational block heater could take a very long time to start and ramp-up to operational speed and voltage.
   2. Any air leaks in the fuel system will cause extended start times.
   3. Weak engine starting batteries can be a source of abnormally long start times.
2. Is there an engine start delay built into the ATS logic?
   1. Typically referred to as Time Delay Engine Start (TDES) this delay will not allow the engine start contacts inside the ATS to close until the time delay has elapsed. This delay is meant to eliminate nuisance starts. Typically settable between 0-60 seconds. Hospital Critical and Life Safety branches are normally set at 0 seconds.
3. Is there a time delay normal to emergency built into the ATS logic?
   1. Time Delay Normal to Emergency (TDNE) means that the ATS will “watch” power on the emergency side for the duration of this time delay to ensure it is acceptable and steady. When this delay is enabled, the ATS will not move to the emergency source until the emergency side power “acceptable” to the ATS for the duration of the time delay. Hospital Critical and Life Safety branches typically have this delay set to 0.
4. Is there a time delay neutral built into the ATS logic?
   1. The Time Delay Neutral (TDN), some manufacturer’s will refer to this delays by differing names, is a means by which the ATS will disconnect from the normal source, stop at neutral (the point where the load is not connected to either the normal or the emergency source), and wait for the time delay to expire before moving to the emergency position. Hospital Critical and Life Safety branches typically have this delay disabled.
5. Is a phase monitor enabled?
   1. A phase monitor is a device that will not allow a transfer of power until the source the load is transferring to is “in-phase” with the source the load is transferring from. This means that both normal and emergency power must have very close to the same phase angles before a transfer of power happens.
   2. The primary job of the phase monitor is to protect heavy motor loads, as in chillers and air handlers, from wear and tear of having power applied out of phase.