Generator enclosure GA: the six lines in the spec that size the box
You open the enquiry for a 1,000 kVA set in an acoustic enclosure, and the first question is how big the box will be. Six lines in the specification decide it: the generator rating, the fuel autonomy, the noise limit, the ambient and cooling conditions, the exhaust silencer grade, and the access and transport limits. Read those six before drawing anything, because together they fix the length, width and height of the enclosure general arrangement (GA), and most of its price.
Everything else in the specification adds detail inside an envelope these six have already set. Reading an enclosure enquiry and returning each of the six with the clause it came from is work Elora Grid does, and it drafts the first GA from them; the engineering judgment on the design stays with your team.
Why these six and not the rest?
Because each one adds length, width or height that nothing else can take away. The engine and alternator set the core. The fuel tank under the skid adds height. Acoustic attenuation adds length at both ends. Cooling air sets the size of the openings, the silencer sets what sits on or in the roof, and the access and transport limits decide whether all of that fits a road load or a shipping container.
The rest of the specification, such as paint system, lighting, control panel options or cable entry, matters to the price but rarely moves the outline. Read it after the envelope is settled.
Rating and fuel autonomy
The rating in kVA, and whether it is quoted as prime or standby, chooses the engine and alternator, and with them the skid length and the width of the core. Check the power factor and the site derating the specification asks for, because a set derated for altitude or heat may need the next frame up.
Fuel autonomy then sets the base tank. A requirement for, say, 24 hours at full load, in a bunded tank under the skid, can add a good deal of height to the enclosure. If the autonomy cannot fit under the skid, the specification may allow a separate day tank, and that is a different GA.
Noise limit and cooling air
The noise limit is usually written as a sound pressure level in dB(A) at a stated distance, often measured to ISO 8528-10. A tighter limit means thicker acoustic lining and longer attenuators on the air inlet and the radiator discharge, and those attenuators are what make an acoustic enclosure longer than the set inside it.
Cooling sets the size of the openings those attenuators sit in. The radiator needs a given airflow at the design ambient temperature, against the pressure drop of the attenuators and louvres. A higher ambient or a tighter noise limit pulls in opposite directions, and the GA has to show the answer: louvre sizes, attenuator lengths and where the hot air goes.
Exhaust, access and transport
The exhaust silencer grade (industrial, residential or critical, in increasing order of attenuation) sets the size of the silencer, and whether it fits inside the enclosure or sits on the roof. A roof-mounted silencer and stack can decide the overall height more than the set does.
Access and transport close the envelope. Maintenance access around the engine, the doors the operator needs, and the position of the control panel set the internal clearances. Then the whole box has to travel: a road transport height limit, a crane lift or a container footprint can force a split enclosure or a different layout, and the GA should say which.
What goes on the tender GA?
The outline these six produce, dimensioned: overall length, width and height, the louvre and attenuator positions, the exhaust outlet and stack height, the doors and access, the base tank and its bund, the lifting points and the cable entry. Note beside each dimension the specification line that set it, so a reviewer can see why the box is the size it is.
Leave the internal framing, the sheet metal details and the fixing schedule for the fabrication drawings. The guide to what a tender GA has to show covers that line in general; for an enclosure, the same rule applies to the frame and panels. Elora Grid drafts the enclosure GA around the genset, with each note traced to its line in the specification, as DWG and PDF for your drafters to check.
Six specification lines and what each one sizes
| Specification line | What it sizes | Where it shows on the GA |
|---|---|---|
| Rating (kVA, prime or standby) | Engine, alternator and skid | Core length and width |
| Fuel autonomy | Base tank and bund | Height below the skid |
| Noise limit (dB(A) at a distance) | Lining thickness and attenuator length | Overall length, inlet and discharge |
| Ambient and cooling | Radiator airflow and opening size | Louvre and attenuator sizes |
| Exhaust silencer grade | Silencer size and position | Roof or internal silencer, stack height |
| Access and transport | Doors, clearances, split or single box | Door positions, lifting points, overall envelope |
- 01Find the six lines. Rating, fuel autonomy, noise limit, ambient and cooling, silencer grade, access and transport.
- 02Take the set dimensions from the quote. Engine and alternator envelope from the engine supplier you are pricing.
- 03Size the base tank. Autonomy at the stated load, with the bund the specification asks for.
- 04Size the attenuation and the openings. Noise limit and cooling airflow together, at the design ambient.
- 05Place the silencer and the doors. Roof or internal silencer, access and maintenance clearances.
- 06Check the transport envelope. Road height, crane lift or container footprint, before the GA is issued.
Common questions
What sets the size of a generator enclosure?
Six lines in the specification: the generator rating, the fuel autonomy, the noise limit, the ambient and cooling conditions, the exhaust silencer grade, and the access and transport limits. The rating sets the core, the fuel tank adds height, the noise limit and cooling add attenuators and openings, the silencer can set the overall height, and transport limits decide whether the box ships in one piece.
Why is an acoustic enclosure so much longer than the generator?
Because the air has to get in and out quietly. The radiator needs a large airflow, and the inlet and discharge openings carry attenuators whose length grows as the noise limit tightens. Those attenuators sit at each end of the set, so a tight dB(A) limit at a short distance adds length that has nothing to do with the engine.
Should the tender GA show the internal frame?
Not in detail. The tender GA shows the outline, the openings, the doors, the base tank, the exhaust and the lifting points, with the dimensions the specification drives. Internal framing, sheet metal folds and fixings belong on fabrication drawings after award, once the design is developed. Detail drawn at tender is detail you may be asked to honour.
Can Elora Grid draft a generator enclosure GA?
It reads the enclosure enquiry, picks out the lines that size the box, and drafts side and end elevations around the engine, alternator and base tank, with each note tied to the clause that asked for it. The drawings come out as DWG and PDF with a change log, and your engineers check the acoustic, cooling and structural design before anything is issued.