The EEI MASS Test for Plant Maintenance Jobs

MASS — the Plant Maintenance Positions Selection System — is the EEI battery for maintenance trades in power plants. It is four tests and 118 questions in 72 minutes of timed work: Reading Comprehension (36 questions in 30 minutes), Mechanical Concepts (44 in 20), Assembling Objects (20 in 15) and Mathematical Usage (18 in 7). The whole sitting takes roughly two hours.

EEI's catalog lists the jobs it screens for: mechanic, machinist, electrician, welder and pipe fitter. If you have seen MASS described as a meter reader test, that is a persistent mix-up — meter reading has its own battery, the MRAB.

The battery in full

Test	Questions	Time	Per question
Reading Comprehension (5 passages)	36	30 min	50 sec
Mechanical Concepts	44	20 min	27 sec
Assembling Objects	20	15 min	45 sec
Mathematical Usage	18	7 min	23 sec
Total	118	72 min

Assembling Objects — the one that is only in MASS

Assembling Objects is the section that distinguishes MASS from every other EEI battery, and the one most candidates have never seen before. You are shown separate parts and asked which of the options shows them correctly put together — a spatial task rather than a mechanical or numerical one.

Forty-five seconds a question is the most generous clock in the battery, which tells you the items are meant to take some thought. The trick that helps most is elimination on a single feature: pick one distinctive part, find its orientation or connection point, and discard every option that gets it wrong before comparing what survives. That is faster and more reliable than trying to assemble the whole figure mentally. Our Assembling Objects demo generates fresh items each time so the shapes cannot be memorized.

What MASS shares with the rest

The other three tests are the ones you will find elsewhere in the EEI catalog, which makes MASS preparation efficient:

• Mechanical Concepts is the same 44 questions in 20 minutes that appears in CAST, CAST-R, POSS and TECH. It is the densest clock in the battery at about 27 seconds a question, and for a maintenance trade it is also the most job-relevant test on the paper. Practise it in full 44-question blocks — see the demo.
• Reading Comprehension is 36 questions across five passages, the same as POSS and slightly longer than the CAST version.
• Mathematical Usage is the short form: 18 questions in 7 minutes on basic mathematical formulas, worth practicing purely for pace. Try the Mathematical Usage demo.

Where MASS came from

The brochure describes a four-year study initiated in 1981 and conducted by the Personnel Decisions Research Institute of Minneapolis, with over 40 electric utility companies taking part. The document itself carries a 2001 copyright and an October 2015 update. That vintage is worth knowing for two reasons: the battery has been stable for a long time, and the published description is authoritative in a way that no third-party summary is.

How MASS is scored

The component scores are combined into one index score, which the brochure says is translated into expected probabilities of successful job performance to support selection decisions. Unlike POSS with its zero-to-15 aptitude index and CAST with its 1-to-10 index, EEI does not publish a numeric range for the MASS index. If you find a site quoting one, it is not coming from the brochure.

The brochure does state that there is no penalty for guessing or wrong answers, so there is never a reason to leave an item blank. And as with every battery in the catalog, no employer publishes the level at which it hires — that decision is made company by company and kept internal. How the index scales work explains what can and cannot be known here.

MASS and POSS together

Plant hiring often runs both batteries: Entergy, AECC and LG&E-KU all advertise a combined POSS/MASS sitting, and the POSS brochure says the two together take about three hours. The overlap is substantial — Reading, Mechanical Concepts and Mathematical Usage are common to both — so the extra preparation for the pair is really just Figural Reasoning on the POSS side and Assembling Objects on the MASS side.

If you are applying into a plant without knowing which roles you will be considered for, prepare both non-shared sections. They are short, they are unlike anything else on the paper, and they are the two places where being unfamiliar with the format costs real marks. MASS practice runs the battery in order, and Complete access covers both plant batteries.

Frequently asked questions

How long does the MASS test take?

72 minutes of timed testing, in a session of about two hours. One EEI-derived description puts MASS administration at about two and a half hours, so allow the longer figure when you plan your day.

What is a good MASS score?

There is no published answer. MASS produces a single combined index whose numeric range EEI does not publish, and employers set their own requirements internally without disclosing them.

Is MASS the meter reader test?

No. MASS is for plant maintenance trades — mechanics, machinists, electricians, welders and pipe fitters. Meter reading is covered by a separate EEI battery, the Meter Reader Aptitude Battery.

What is the hardest part of MASS?

By clock pressure, Mechanical Concepts and Mathematical Usage. By unfamiliarity, Assembling Objects — most candidates have never attempted a spatial assembly item before sitting down, which is the easiest problem on this list to fix.